When young Pear arrives at Kopolka's mental asylum on the day of his mother's death, he is summoned to a cavernous midnight rendezvous where he meets Mystery, an enigmatic patient with a penchant for philosophy. He is soon tricked into her service which, at first, requires little more than helping her torment a school tyrant and retrieving a shipwreck for a seaboard shelter. All seems well, particularly during his sojourns to the mollifying Water, a fantasy, underwater world in which he finds himself a whale in the company of erudite octopus Mr Octaveley. Soon, though, he discovers that Mystery harbours dangerous delusions of her own and, as the price of replacing his mother becomes ever more challenging for his shy, quiet nature, the lines between reality and fancy begin to shake. The question is, will Pear let them crumble or can he fight back?