Orphans Albert and Victoria Wiggins leave the orphanage there they have been living since their parents' deaths and go to live on the farm of their inventor uncle, Sir Joshua Cranberry. There they find themselves initiated into the Centauri Network, a global communication network of kids run by Jemma, the twelve-year-old daughter of their uncle's assistant. Pursuing the kids are the agents of criminal mastermind Neville Savage who wants the kids who can get him access to the contents of a crashed top-secret satellite that their father had worked on.

A report from Ollie Bergmann, the Centauri Network's member in Hamburg, about a mysterious illness affecting endagered white-tailed eagles on Rügen Island takes Sir Joshua to Germany along with Albert and Vicki. Savage, and his illusionist accomplice, are behind the plot and find himself up against a group of local children who have dedicated themselves to protecting the remaining birds.

In Sydney, one of Savage's cohorts steals a journal belonging to Leonardo DaVinci. Savage hopes to use one of the inventions described in the jorunal to create a duplicate of the famed Mona Lisa and use this forgery to replace the original which is currently on display in a museum in Amboise, France. Meanwhile, Sir Joshua travels with Vicki and Albert to an inventors' congress in Amboise where he is to unveil his solar-powered car. There the kids get to meet Centauri Network member Marie and Pierre, whose grandfather is the director of the museum and a leading expert on Leonardo da Vinci. When Pierre's grandfather is abducted, the children must work to rescue him from a secret lab beneath a castle in the Loire Valley before Savage can learn the secret to the duplicator.

Neville Savage's search for a sunken Spanish galleon off the island of Mallorca attracts the attention of the Centauri Network when his sonar tests drivers all the fish from the bay. Centauri member Francesca, the daughter of one of the local fisherman, contacts Jemma to report the trouble bringing the two sides into contact once again. The assembled Centauri children race against Savage's forces to recover the priceless cup of Cala Figuera, an endeavour that will take them from Spain to the Swiss Alps where Vicki and Albert join up with Centauri members Lucia and Guido to solve the riddle, recover the cup, and stop Savage.

Before returning to Australian, Sir Joshua, Albert and Vicki stop in Yorkshire England to visit his aunt Edith who is having trouble with her neighbour. The Centauri network is soon called upon to track down the neighbour's stolen horse. It is quickly discovered that Savage's crime syndicate is behind the theft but Albert and Vicki, working with the neighbour's daughter Sarah, are unable to stop the horse from being smuggled out of the country to Poland. Polish Centauri member Jan is on hand to help in the search but Savage is able to stay one step ahead of the kids who are thwarted at every turn in their search for the elusive horse.

Sir Joshua, Albert and Vicki return triumphantly to the farm in Australia knowing that although Savage remains at large, all of his accomplices have been arrested. The Centauri Network welcomes three new members; Brian and Karen from Melbourne and Hoshi from Japan. Now working out of an island on Sydney Harbour, Savage has been joined by a 19-year-old hacker and his little sister Sandy. Sir Joshua's latest invention, a boring machine, uncovers massive gold nugget on his neighbour's property but Sandy is able to infiltrate the farm allowing Savage to compromise the security system and steal the nugget from inside Centauri headquarters. With Savage appearing to be on the verge of destroying the Centauri network once and for all, new allies help to finally bring him to justice.