A smirking boy shuffled past the door, and Marion, hands shaking, quickly turned the key in the lock. It was Cotterson, the boy from Sewers Canal who wanted to burn the Sobraon. Her heart jolted.

The barge had delivered the Forty Thieves onto the ship!

Marion's life is anything but ordinary. The daughter of the principal, Captain Neitenstein, she is the only girl aboard a magnificent floating boys' school, anchored permanently in Sydney Harbour in the late 1800s. Her best friend has boarded a steamship to France and now it's just her and this ship full of ragtag schoolboys. One night, Marion discovers that a new student, Alexander Walker, is escaping the ship to meet up with his vicious gang, the Forty Thieves. Marion bravely follows Walker into the frightening Rocks neighbourhood to investigate...What are the Forty Thieves up to and will Marion be able to stop them before it's too late?

Based on the real life Marion Neitenstein, this middle-grade 'faction', which offers an immersive and historically accurate experience of an unusual nineteenth-century institution for neglected boys. Marion's middle-class life is contrasted with Sydney slum life and wharf culture. Other important real characters appear, including businessman Quong Tart and the head of the Forty Thieves gang Joseph Bragg.

The author used primary sources to research the story, such as old gaol inmate records and even Quong Tart's original menus, and delves into these sources in the endmatter, covering topics such as the Nautical school-ships Vernon and Sobraon and their captains, the Rocks, Quong Tart and more. The text is accompanied by real photographs from the ship, portraits of three Sobraon boys from the admissions book and images of Sydney street scene from the period.