Winston calls Dianne and her sons back from their vacation informing them that UBRI has won the contract to construct ORCA City and their plans threaten a nearby fish breading ground. Dianne, as ORCA's new environmental officer, quickly calls a stop to the construction and begins a environmental study of the site. A dive to collect samples sees Jason become trapped under a fallen strut. As a rescue party is assembled, Charlie calls Neri who comes to save Jason as his air is about to run out. Dianne takes her case against UBRI before a tribunal who rule in her favour, stopping UBRI's construction. Dr. Hellegren's plans to destroy the breeding ground are thwarted by Neri. Hellegren warns Jason and Brett not to interfere with him.

Brett talks Jason and Neri into looking for a way into the spacecraft they found buried on Neri's island their search is unsuccessful. Brett and Benny meet Cassandra, a new arrival from ORCA's sister station near Florida. Cass takes out a sailboat, but with a storm coming and a damaged sail, she seeks shelter on Neri's island. The following day Neri finds an entrance to the spaceship that was uncovered by the storm. When Jason and Brett come to the island, Cass sees them with Neri before fixing the sail on her boat and heading back to ORCA. Distracted by the sight of Neri in the water ahead of her, Cass is struck by the boat's boom and is knocked unconscious. Back on ORCA an anxious Jason and Brett discover Cass has amnesia and cannot remember what happened to her. Jason tells Brett to become friends with Cass to keep her from telling about Neri if she gets her memory back. Dr. Hellegren goes to visit his daughter at her boarding school, she pleads with him to be allowed to spend her vacation at home.

Jason and Brett steal a pump from UBRI supplies on ORCA so they can pump out the spaceship. Cass and Brett trade practical jokes but when they team up to get Cass's sister Morgan, they also catch the Commander in their soapy trap. Jason is teamed up with Sallyanne for a training exercise, but their first drill does not go well. With the spacecraft pumped out, Neri and Jason enter the ship. They are joined by Brett, who has been scrubbing the floors on ORCA for his role in the practical joke on Morgan, and the trio come across a person in a sealed chamber, still alive.

ason and Brett are about to force the chamber open when Neri finds the controls that open the chamber and revive it's occupant. He comes to and says his name is Kal. He is shown around the island where he seems to be content to live. Brett and Jason are surprised when Kal says he will take a subordinate role in relation to Neri, as is done on his own planet. Benny covers for a girl caught cheeting on an exam and is also disqualified. Lena Hellegren makes a surprise appearance at UBRI forcing her father to take her home where she convinces him to let her remain instead of being shipped off on vacation by herself.

Concerned about Kal's development, Neri asks Jason to talk to him. After telling him to stay on the island, Kal follows Neri to ORCA. Brett, Benny and Cass are given diving lessons for their failed practical joke on Morgan. After their lesson, Benny sees Kal aboard the boat starting the motor and then diving overboard, he tries to tell people what he saw be no one will believe him and instead accuse him of starting the boat. Dr. Hellegren brings Lena to ORCA where Brett tells her about some of the things her father has done but she won't believe them.

Hoping to keep Kal from making any return trips to ORCA, Jason suggests to Neri that she show him around the spaceship which he has been interested in. Winston's inability to swim is made an issue of by Kellar and UBRI, threatening his job on ORCA as they hope to replace him with one of their own. Fortunately, Benny discovers a provision is the regulations forcing the commander to give Winston a week to meet the qualifications. Neri brings Jason and Brett back to the ship where she and Kal have made a discovery. An interface with the ship's computer gives Neri access the ship's log written by Kal's mother. She explains to the group about a mission requiring the assembly of nine pieces of "Synchronium" which once put together will have the power to heal the Earth's oceans. Neri asks Jason and Brett to help her look for the Synchronium but they must no tell anyone else. Believing that Neri is close by to assist him, Winston passes his swimming test.

Neri goes to ORCA to see how Jason and Brett are going with their search for the Synchronium. Dianne takes the opportunity to ask her to help Winston with his dive test which she agrees to do. When Neri doesn't return to the island on time, Kal takes the opportunity to go back to ORCA. On ORCA, Kal manages to get signed up for Morgan's fitness class (she's very impressed with him) and gets a date with Marika, which Jason is able to speed him through. Neri helps Winston through his test by getting him to believe in himself. After Lena's visit to ORCA, Kellar warns her that her curiosity may reveal things about her father she might not want to know.

Neri awakes on the island to find Kal missing, he's gone to ORCA. Jason and Brett introduce Kal to Diane and Winston. Shortly after, Neri arrives and tells Diane about UBRI's plans to use explosives on the ocean floor in their construction. Diane is not happy and takes the issue before the tribunal but unfortunately they rule in favour of UBRI and allow the blasting to proceed. Jason and Brett begin searching HELEN for reports of UFOs and meteorite impacts that may help them locate the Synchronium pieces. Neri senses something wrong with the oceans but cannot be more specific. Successful in their search, Jason, Brett, and Neri venture inland to retrieve the first piece of Synchronium. Lena accesses her father's locked computer files. Kal beats Benny, the youth champion, in a game of trigammono.

Brett locates another piece of Synchronium but interrupts Jason's training exercise to tell him the news. UBRI has also located the piece and mount an effort to retrieve it. Lena is back on ORCA looking for clarification about her father, she learns nothing from Brett but does meet Kal. Jason, Brett, and Neri go after the second piece of Synchronium, it is far inland and they must go by camel. Arriving after UBRI, who have already recovered the Synchronium, the trio is spotted and pursued by Kellar who they are able to elude on their sure-footed camels. Dr. Hellegren begins studying the piece of Synchronium and discovers that it generates a tidal force.

Neri moves the Synchronium piece to her secret underwater cave to keep it safe. Benny's father chastises him for spending time with Brett and Cass instead of studying. Cass finds a young boy on ORCA who swam to ORCA from the ship that was taking him and his family home after they were refused refugee status, she keeps him a secret and brings him food. Brett and Benny go in search of sunken treasure but when a valuable piece of equipment falls overboard, Benny goes after it and runs out of oxygen. Charlie calls Neri to rescue him revealing to him her presence. Benny lies to the commander about the incident to keep Neri a secret. Cass' stowaway is discovered and he is turned over to immigration officials. Lena gains access to her father's files about Neri.

A trip to ORCA prompts a discussion between Neri and Kal about feelings. Cass is beginning to remember about her time on Neri's island in her dreams. Brett takes Benny to the island to see Neri and Kal and Jason arrives soon after having discovered the location of another piece of Synchronium deep in the ocean. Neri is anxious to retrieve it and sets out by herself. The boat taking Brett and Benny back to ORCA breaks down, and with strict instructions not to go to ORCA, Kal abandons them in the middle of nowhere. Fortunately, Charlie alerts Neri, who was unsuccessful in her attempt at retrieving the Synchronium, and she comes to their rescue. Back on ORCA Brett is hassled by Moose, a bully who demands his new satellite navigation unit. With Jason and Brett assisting her, Neri retrieves the Synchronium from the ocean depths just moments before UBRI arrives on the scene. Brett is again confronted by Moose but Kal, acting on the lesson he received on loyalty after abandoning Brett and Benny, defends Brett against Moose and his cohorts.

Neri continues to teach Kal about feelings. Cass is still having her dreams about her time on Neri's island and now remembers Brett being there. Lena overhears her father and Kellar talking about their plans for creating a news bulletin to lure some of the kids from ORCA to an island to find out exactly what they know about the alien device. Jason is uneasy about his helicopter flight test and is unable take the controls. Kal searches the spaceship for a gift left to him by his parents. Benny and Brett arrive and find him playing a strange musical instrument and crying, Brett explains to Kal why people cry. Seeing the news bulletin created by UBRI, Brett and Neri head off to the remote island looking what they believe to be another piece of the Synchronium. Lena arrives on ORCA to warn the Bates brothers about the trap but she is too late to stop Brett, she does find Jason and warn him. Needing to get to Brett and Neri quickly, Jason goes on another helicopter test with Morgan and diverts to the island to warn Brett and Neri. Upset by his failed plan, Dr. Hellegren suspects a leak in the UBRI chain of command but it is Kellar who learns who tipped off their plan.

Neri receives a message from Mera in a dream warning her that time is running out. Neri goes to ORCA where she warns Dianne that UBRI's development must be stopped. Kellar tells Hellegren of her suspicions about Lena, but he won't listen to her and tells her to not to question his daughter. Jason is forced to tell Lena all about Neri and their search for the Synchronium. Dr. Hellegren orders the construction of ORCA City to be sped up by increasing the yield of the explosives. Cass is sent to a psychiatrist to help her understand her dreams, what she remembers however is quickly reported back to Dr. Hellegren who observes her next session. Cass returns to ORCA with a restored memory and demands to know the truth. She is taken to meet Neri and promises to keep her a secret and aid in the search for the Synchronium. With evidence of his daughters actions, Dr. Hellegren confronts Lena, she admits what she's been doing and leaves home after he says she is no longer his daughter. Kal experiences fear when Neri is threatened by a large underwater explosion. Winston believes the continuous explosions may threaten the stability of a nearby fault line and cause earthquakes.

HELEN is not being cooperative in the kids' search for more pieces of the Synchronium. Meanwhile, UBRI has located another piece. With no where to go after leaving home, Jason and Brett convince their mother into letting Lena stay with them on ORCA. Lena is taken to meet Neri and Kal on their island and after returning to ORCA, she is able to find the location of another piece of Synchronium from HELEN. Unfortunately, when they arrive at the location pinpointed by Kal, they discover that once again, UBRI has beaten them to it. Plans are quickly made to get the two pieces that UBRI has in their possession. Neri want's to go on the raid of UBRI headquarters and Jason, concerned for her safety, begrudgingly agrees to let her come along but then leaves with the others a day early to keep her from coming. Neri comes to ORCA the next day to see how the plans are going and discovers that she's been lied to and she angrily goes back to her island to wait. Entering the UBRI complex, the two pieces of Synchronium are recovered but one is lost trying to escape UBRI security on the way out. Winston finds evidence of a possible fault line but the commander is not convinced. When Neri expresses her concern for Jason, Kal's jealousy of their relationship begins to surface.

Winston is excited about the arrival of Camilla Sabato to ORCA. She is a science writer but more importantly, a close friend. Winston gives her a tour of ORCA but afterward Brett catches her making a secret transmission to Dr. Hellegren telling him that she will be looking for information about his "Ocean Girl." Brett informs Dianne and Winston who see that Camilla leaves ORCA. Kal finishes at the top of his class in a fitness competition, he returns to the island to tell Neri but finds her once again preoccupied with Jason. Kal's jealousy surfaces again and after telling Jason that he is no longer welcome on the island, he moves back into the spaceship. Neri is concerned about the condition of a nearby coral reef, she and Jason go to film the site (Jason skips out on a party that Sallyanne asked him to) hoping to gather evidence to prove that ocean life is being destroyed by UBRI's construction of ORCA City. A large earthquake strikes, opening the fault line near ORCA.

Dianne demands that a tribunal hearing be convened to stop UBRI's development, but Hellegren argues that there is no connection between the earthquake and UBRI's explosions. Another piece of the Synchronium is located by Lena, and Brett and Cass are sent to Neri's island to get Kal to pinpoint it's location. Venturing inland to retrieve the piece, Neri, Brett and Cass encounter a farm family with a blind daughter (Petra Yared). After discovering the Synchronium capsule to be empty, the trio are surprised to find that the Synchronium piece is a prized possession of Patti. After spending time with Patti, she gives Neri the Synchronium piece. When Lena encounters her father on ORCA, she threatens to go public with his work if he makes life difficult for her on the station. Dianne is upset to discover that canisters of radioactive materials are being stored in the school section of ORCA. When a tremor strikes, the canisters break open threatening Benny who is in the otherwise deserted computer lab. Jason goes against regulations to get him out and afterward he is praised by Commander Wellington who also chastises Morgan for her "by-the-books" approach to the emergency.

Brett tries unsuccessfully to get Kal to come out of the spaceship. Dianne is granted a tribunal hearing to voice her concerns about the effects UBRI's construction is having on the fault line. During the hearing a tremor hits causing panic on ORCA and causing Charlie to beach himself. Neri recruits her friends on ORCA to try and rescue him. Jason leaves his post to help out and Sallyanne must cover for him when the Commander asks her where he is. The tribunal allows UBRI to continue their construction, but without blasting. Kal comes to ORCA looking for Brett but ends up talking with Sallyanne since everyone else is helping with Charlie. Needing additional help to free Charlie, Jason recruits Winston who helps place a sling under Charlie so that he can be towed off the sandbar. Returning to the island, Kal asks Neri why he wasn't asked to help with Charlie, unhappy with her answer, he walks away. On a secluded sandbar, Kal is observed and photographed by UBRI.

Kellar shows Dr. Hellegren the footage she took of Kal on the sandbar, he quickly recognizes who Kal is and wants to capture him. After another of Kal's outbursts at Jason, Neri tells him to change his attitude or leave the island, Kal chooses the latter. A causal remark by Dave Hartley to Dianne has Brett thinking he may be interested in her. Brett recruits Benny to write a love note hoping to get the pair together (for his own selfish reasons mind you). Unfortunately, Jason inadvertently gives the note to Sallyanne who thinks Jason has finally taken notice of her. When he tells her of the mistake, Sallyanne is crushed. Brett tries to end the fiasco by throwing out the note but is is retrieved by Delores, a girl he's been hounded by all day. Kal is caught by Dr. Hellegren and taken back to UBRI headquarters where Hellegren begins the process of convincing Kal to trust him. Worried about what has become of Kal, Neri, Brett and Jason search the island for him.

Neri continues to look for Kal but Jason suggests Kal is just trying to teach them a lesson by staying away. Neri receives another warning from Mera. Lena locates another piece of the Synchronium but without Kal to pinpoint its location, she gets HELEN to calculated possible sites. Dr. Hellegren gets Kal talking about Neri, Jason and ORCA. Kellar leads a UBRI team to retrieve the Synchronium piece while Dr. Hellegren stays behind to talk with Kal. The kids locate the Synchronium at the bottom of a seaside cliff and Jason repels down to get it as UBRI, who have been observing the kids, closes in. The others must flee with Neri to ensure safety, forcing Jason to hand over the Synchronium to Kellar. Jason overhears Kellar saying that they have Kal. Dr. Hellegren gives Kal the choice to leave or to stay with him and work towards possessing the Synchronium themselves. Kal, captivated by the power he is being offered accepts Hellegrens proposal to work together.

Kal is in the lap of luxury at UBRI, his room filled with all sorts of toys and games. Kellar, making reference to his failed relationship with Lena, angers Dr. Hellegren by suggesting he is treating Kal like an "obedient son." Hoping to find out where UBRI is keeping Kal, Cass and Brett take to the ORCA air ducts planning to break into UBRI's offices on OCRA. Discovered by UBRI security, they must quickly retreat at which time Brett loses his ID. UBRI identifies the intruders from Brett's ID and Dr. Hellegren seizes upon the opportunity to help him return Kal to his friends. About to release Kal, Dr. Hellegren tells him he is to discover where Neri keeps the pieces of Synchronium and report back to him, he also teaches Kal how to lie, and again promises Kal control of the island if he cooperates. Cass and Brett return to the air ducts in onother attempt to find out where Kal is being kept. Kellar is prepared and makes sure the two can hear her as she describes in detail UBRI's plans to relocate Kal. Using this information, the kids are able to "rescue" Kal from the UBRI truck transporting him. Back on the island, Brett says he is glad things are "back to normal" but at the same time, Kal is swimming out to talk to Dr. Hellegren who is disguised as a fisherman nearby.

Neri has Kal promise not to leave the island again. Lena uses HELEN to locate another piece of the Synchronium. Mera appears to Neri to again warns her that time is running out. The next day, Neri and Kal are on ORCA, but when asked to pinpoint the landing area of the Synchronium, Kal says he cannot. Kal tells Neri he is going back to the island to have a swim and think about problem but he instead goes to see Dr. Hellegren to tell him about the new piece. Hellegren isn't anxious to sent UBRI forces after it, instead preferring to let the kids find it and then take all the pieces at once after Kal discovers where they are hidden. Lena does her best to pinpoint the location of the Synchronium, but must use more of HELEN's resources to do so. Unfortunately an earthquake hits at that moment and the Commander quickly discovers the extra strain on HELEN when he is unable to access HELEN. As punishment for their actions, Lena, Cass, Brett, and Benny are assigned to clean-up detail-with Morgan as their supervisor. Neri ventures into the outback on her own to recover the Synchronium but succumbs to the heat. She is found by an aboriginal girl who takes her back to her family's campsite. There she is told a story about a water spirit who crashed to earth creating the water hole before them. Realising what the story means, Neri dives to the bottom of the water hole and finds the piece of the Synchronium. Finished with their clean-up duty, Cass takes out her frustrations on Morgan. Neri, exhausted from her walk back to the shore and her swim to the island, is met on the island by her friends. That night, as Neri sleeps, a spaceship lands on the island-Mera has returned to help her sister.

The cadets' exam results are in and after looking at hers, Sallyanne tells Jason he would be better off with another partner. Mera reveals to Neri and her friends that Charlie's song is the trigger that activates the Synchronium. Kal overhears this and quickly goes to tell Dr. Hellegren. Hellegren meanwhile has to contend with his financiers who are anxious for results. Mera is taken to ORCA and introduced to Benny, Cass and Lena. Neri and Mera talk Lena into stealing the key her father wears around his neck—it is the only way to gain access to the Synchronium that UBRI has. Outside the Hellegren home, Kal makes a surprise appearance wanting to help. After Lena gets them into the house and Neri is about to get the key, Kal intentionally knocks over a vase waking Hellegren. They are all able to escape but do not get the key. Disappointed about her scholastic performance so far, Sallyanne wants to quit but decides against it after saving Jason when a bulkhead is breached.

A large quake hits keeping Lena from accessing HELEN to look for more of the Synchronium. Cass and Benny sneak into the UBRI offices on ORCA where they overhear Dr. Hellegren talking to a Mr. Lee about a trade for a piece of the Synchronium that Mr. Lee has. Wanting to get this new piece before Hellegren, Cass, Benny and Lena gain entry into Mr. Lee's office building to retrieve the Synchronium. Cass and Lena are caught by security, but Benny, unsure about whether or not to flee the building, goes back and rescues the girls from Mr. Lee's office. Jason and Brett are told about the Synchronium in Mr. Lee's possession and they make plans to steal it when Mr. Lee brings it to ORCA to give to Dr. Hellegren. Meanwhile, Brett goes back to the island to search through the ship one last time, he is joined by Mera and Kal. Separating himself from Mera and Brett, Kal sneaks off to follow Neri hoping to discover where she hides the Synchronium. Charlie warns Neri and Kal is discovered. Back on the island, Mera once again voices her disapproval of Kal's actions. Winston is honoured by having the newly discovered fault line named after him.

The growing frequency of the seismic tremors causes Commander Wellington to call for voluntary evacuations of ORCA personnel. Cass tells Morgan to "drop dead" when Morgan gets after Jason for wanting to skip a survey dive. Jason's dive with Morgan ends abruptly when Morgan is stung by a stonefish, requiring her to be rushed back to ORCA. Cass feels guilty for what she said to her sister earlier. Sallyanne tries to talk to Jason about how she feels about him but he dismisses her to join his friends who are preparing to intercept the Synchronium transfer from Mr. Lee to Dr. Hellegren. Brett stows away on the UBRI vessel and when the are out at sea, he disables the craft and steals the Synchronium piece. Brett jumps overboard where Neri and Mera are waiting just as the Coast Guard arrives to board the UBRI vessel-Benny faxed them to tell them about UBRI's involvement with Opal smuggling. Having losing another piece of the Synchronium, Dr. Hellegren tells Kal that his most important job now is to locate where the Neri is hiding the Synchronium pieces.

The effects of the new "Winston Seth" fault line are being felt all around the Pacific Rim as evacuations on ORCA are taking place. Lena locates the final piece of the Synchronium. Mera grows more suspicious of Kal's frequent disappearances but Neri once again defends his behaviour. After Sallyanne confronts Jason, Lena tells him that he should tell Sallyanne about Neri as she is his only close friend who doesn't know. He kids venture inland to recover the Synchronium, UBRI is also searching in the area but it is Neri who recovers the final piece. Neri gives the Synchronium piece to Jason to take to the underwater cave. Kal observes the pair leaving and discovers the location of the cave. He quickly reports back to Dr. Hellegren who, after dismissing Kal's request to have his side of their bargain upheld, sets out to recover the Synchronium. As Kal is bringing the pieces to the surface for Hellegren, Charlie warns Neri about what is going on, but when she gets to the cave, the Synchronium is already gone. Jason tells Sallyanne the truth about Neri but she doesn't believe his incredible story about a girl from outer space. Neri tells Jason and Brett the consequences of the Synchronium being used by the wrong people.

A large quake prompts the commander to call for an evacuation of all ORCA personnel under the age of 18. Dr. Hellegren is putting the Synchronium together when Kal demands that he be made the ruler of Neri's island as he was promised, Hellegren again brushes off Kal and has him escorted back to his room. Anxious to get the Synchronium back from Dr. Hellegren, Neri goes to get Jason. He is out on a dive mission with Sallyanne, and when Neri surfaces Sallyanne is there to see her. Angry about the way he is being treated by Dr. Hellegren, Kal attempts to steal a piece of the Synchronium, he is quickly caught by UBRI guards and taken back to his room. Back on ORCA, Sallyanne is introduced to Neri and Mera and plans are made to recover the Synchronium. Getting away during the confusion surrounding the evacuation, the kids are able to make it to UBRI's pier on the mainland. However, they are soon spotted by Kellar and are left tied (Dr. Hellegren taking Lena with him) up as the UBRI vessel heads out to sea. Kal escapes from UBRI and arriving at the pier, he unties the others. As Dr. Hellegren prepares to activate the Synchronium, Neri and Mera surface and plead with him not to proceed, even offering themselves for his to study if he stops. With her father preparing to unleash the power of the activated Synchronium, Lena jumps into the now seething and churning ocean to force him to stop or risk killing her as well. As Hellegren hesitates unsure what to do, Kellar pushes him aside to lower the Synchronium into the ocean. Just before it impacts, Kal surfaces and grabs the Synchronium and with Neri and Mera take it back to the island as a dejected Dr. Hellegren must admit defeat. Back in the safety of the island, Neri and Mera activate the Synchronium reversing the damage done to the Earth's oceans. Neri and Mera make a final trip to ORCA where Dianne and Winston are told about the Synchronium. After saying their goodbye's, the girls return to the island where Kal and Mera b