‘Petrel leaned on the rail, watching the ice cave and stamping her feet for warmth. The berg came closer. That’s when she saw him. Laid out on the ice like a dead fish, with a scattering of snow covering his face. A boy, where there should have been nothing but the memory of winter. A frozen boy.’

Twelve-year-old Petrel is an outcast, the lowest of the low on an ancient icebreaker that has been following the same course for three hundred years. In that time, the ship’s crew has forgotten its original purpose and broken into three warring tribes, the Cooks, the Officers and the Engineers. Everyone has a tribe except Petrel, whose parents committed such a terrible crime that they were thrown overboard, and their daughter ostracised.

But Petrel is a survivor. She lives in the dark corners of the ship, trusting no one, speaking to no one except two large grey rats, Mister Smoke and Missus Slink. That is, until a boy is discovered, frozen on an iceberg, and brought onto the ship. No one knows where he has come from, and when he recovers consciousness he claims to have forgotten even his name. The tribes don’t trust strangers; they haven’t seen one for three hundred years. But Petrel saves him and hides him away in the forgotten corners of the ship, hoping he will be her friend.

What she doesn’t know is that for the last three hundred years, the ship has been guarding a secret. A secret that could change the world. A secret that the boy has been sent to destroy, along with the ship and everyone on it.

‘It’s the Ghosts!’ cried Sharkey, and his blood ran cold. ‘It’s the Hungry Ghosts! And they’ve found Rampart!’

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 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?

‘The verses dried up in Gwin’s mouth. Papa put down his fiddle. Nat looked defiant, though he was trembling, too.

One by one, three wild mountain men stepped off the rope ladder and into the cave.’

Gwin is a Fetcher. With her papa and twin brother, Nat, she travels West Norn, bringing joy to its downtrodden people through song and story. But ever since Mama died, it’s been hard to keep the joy alive.

Proud and defiant, Fetchers have always been hunted by the Devouts for preserving the old ways. So when devious Brother Poosk captures Papa, Gwin must rescue him – whatever the cost.

Meanwhile, the Oyster’s crew and the Sunkers lay siege to the Citadel. But without their Sleeping Captain, can they ever win against the ruthless Devouts? Can Petrel, Fin, Sharkey and Rain ever bring light back to such a dark world?

The thrilling conclusion to The Hidden Series.