A hanging always draws a crowd. But not everyone there has come to jeer at the condemned man. George Kevill's young son Barney is in the front row, and he knows his father is innocent. There are others there who know George is innocent, too - and the men who set him up have every reason to want to silence his boy... Narrowly escaping the clutches of the sinister Nasty Man, young Barney finds sancutary at the London Aquarium amongst his father's bohemian friends: they will protect Barney and seek to uncover the conspiracy behind a dark secret that lies at the heart of the Victorian establishment.