Eve's attempts to help her sister KT pass for human are derailed when a miraculously recovered Katherine returns to Calimov. To Nick and Eve's horror, Katherine reveals her new range of childbots, which have been placed with local families. To prevent Katherine restoring KT to factory settings, Eve smuggles her out of Calimov and back to the Clarke house. But with Will and Lily insisting KT is returned to Calimov, Eve and her sister are forced to take matters into their own hands. The situation escalates when Katherine's childbots start to malfunction and it is KT who comes under suspicion, admitting she has no wish to pass as human. In order to make Eve prove she loves her sister as she is, KT wants Eve to reveal her own robot identity to the world. Trapped inside the house by the childbots, and with police and reporters gathering outside, the gang's worst fears have been realised. With Eve about to admit her secret to the world on live TV, can Will's nanobots save the day?

Rebecca and Nick are desperate to get to the bottom of Will's nanobot problem, so they take him into Calimov to run some tests. Whilst there, Nick insists that Katherine deactivate KT after the trouble she has caused, but Katherine has other ideas. Meanwhile, Abe is disgruntled after Lily refuses to help him with his homework - she's more interested in her date with Cain. Maddy has her hands full preparing for the arrival of the new baby and tells Abe that it's time he grew up and took some responsibility for himself. A dejected Abe goes to Eve for help. As Eve completes his homework, Abe wonders aloud what's so special about babies - why do they get everyone's attention? After researching human child-rearing, Eve cites 'helplessness' as the main reason. Inspired, a scheming Abe fakes being ill to regain Maddy's attention, but his plan backfires. Suspecting Abe has appendicitis, a concerned Maddy calls an ambulance.

For the umpteenth time, Eve defeats her friends at gaming, singing a football chant in triumph. Eve explains how, in a matter of nanoseconds, her predictive software allows her to always choose the best possible course of action - hence the winning streak. But it cannot predict random events like lottery numbers, much to Abe's disappointment. Unknown to the gang, Cain waits outside with Michael Hoffman, the son of the late Lord Hoffman. In their attempts to find rogue robots, Cain pitches his theory that - given the multiple incidents involving robot activity at the Clarke house, plus Nick's prior history with Mary Douglas - this is a good place to start. When the doorbell rings, Eve answers to find Cain and Michael. Detecting their concealed EMPs, she slams the door on them. Spooked by this odd behaviour they break in, fearful that there may be another robot siege in progress. Once inside they learn that Eve is the robot and blast her with their EMPs - only for time to rewind. This has simply been a simulation in Eve's predictive software! Eve runs multiple simulations, trying to find a way to stop Cain and Michael discovering her robot nature, but in each one her identity is exposed, and Cain and Michael destroy her. With time running out, Eve recruits the Will and Lily simulations. Lily speculates that Eve is experiencing anxiety - she has become so human that it has caused her predictive software to malfunction. Eve must disable the software and go it alone. Although Eve manages to evade discovery, neither she nor the gang realise that, while inside, Cain has bugged Nick's computer and is one step closer to the truth.

Mary resorts to extreme measures to head off the threat of Cain and Price, enlisting KT to help her temporarily transfer her consciousness to Eve. With KT missing, a distracted Nick and Katherine welcome back Zac, who is helping them answer questions about how Mary was able to duplicate his personality. Excited about Zac's return, Eve suggests he join the gang's picnic that afternoon. To everyone's surprise Zac brings his new girlfriend, and for the first time Eve experiences jealousy. Spotting KT hovering nearby puts Eve on high alert. Operating under Protocol Zero, KT is Mary's automaton, and is primed to execute her mother's plan.

Having been unknowingly possessed by Mary, Eve is on high alert. Matters are made worse by the fact that her memories of recent events are corrupted. Could Eve's actions be down to a sleeper virus, or - as Will suggests - has Mary found some way to cheat death? Eve's investigation is put on hold when Abe embroils her in a family drama. The Watsons have been invaded by their crotchety grandma Gloria, who is irate having discovered Abe's online competition to name his newborn brother. Eve witnesses the Watsons' meltdown as Gloria reveals that she never approved of Maddie and Viv's marriage.

The discovery that Mary has cheated death throws the gang into chaos. If Mary were to take control of Eve permanently, she would be unstoppable. Sending KT as bait, Mary lures Eve to a secret bunker beneath Calimov. Will and Lily are horrified to discover that Mary has built herself a body out of the reclaimed childbots. Mary wants Will to bring her inanimate body to life! The ultimatum for Will: do as Mary demands or risk Mary deleting Eve and KT's memories. Unable to bear the thought of losing his friend, Will ignores Lily's pleas and uses his nanobots to force Mary's disembodied consciousness into her robot body.

Will and Lily aren't speaking. Worse still, Will is suffering adverse side-effects from protecting his friends from the rogue KT. Nick, fearing that he might not find a way to repair Will's nanobots, puts Eve on the spot, asking her if she can find Mary. Knowing the danger Mary poses, Eve lies - and tracks her mother down in secret. Meanwhile, cajoled by Abe, Lily finally softens and visits Will just as he takes a turn for the worse.

The Clarke household is in crisis. Will's nanobots are rapidly failing, and Nick is at a loss. Determined to save his son, Nick lays aside his initial suspicions when Katherine appears with a hi-tech solution. Will comes round and, despite a nano-hangover, seems well. But, as Nick knows, he is not out of danger yet - Katherine has supplied only a temporary fix. Heeding Nick's warning, Eve tracks down Peterson with Abe in tow.

The world is changing. As Eve tries to prevent a war between humans and robots, Will struggles to control his nanobots and his feelings for Lily, and Mary plots revenge from beyond the grave...