Sharkey was born on a fortunate tide, and everyone on the giant submersible Rampart knows it. He's a hero, a future admiral, beloved by the ancestors. The trouble is, it's all based on a lie, and now Sharkey is thirteen, the whole thing has begun to fall apart. He's been a fake hero for years, but when tragedy strikes, he must become a real one. And he has no idea how to go about it.
Meanwhile above water, Petrel, Fin and the crew of the Oyster are on a mission, a mission to defeat the Devouts and bring knowledge back to the world, a mission they have no idea how to carry out. When the Captain of the Oyster comes up with a plan, Fin and Petrel have no choice but to accompany him - no matter how ridiculous or how dangerous the plan seems .
Can the Sunkers and the Ice Breakers put aside their differences and work together? Or will the Devouts finally catch up with them all?