Thirteen-year-old genius Eva Johnson doesn't want to move to London with an aunt she barely knows. Eva's inventor father says he must travel to find work, but why is he being so mysterious about it? Surely he realises that guarding her sister Ann's secret identity is hard enough in rural Norfolk. Lots can go wrong with a robot simulant - especially when they're a five-year-old who's an expert on the Vostok space programme.

Struggling with attending school for the first time, Eva questions whether Papa is doing the right thing for their family. When Ann is kidnapped during a trip to the science museum, Eva will do anything to rescue her before she's handed over to a ruthless robotics company. Eva and her new friend Rokas track Ann to an eerie abandoned military bunker where disturbing secrets emerge. Eva could lose not only the father she admires, but also the kooky little sister she loves more than anything in the world.

Can Eva keep her unconventional family together when everyone else sees her sister as less than human?