In this sequel to On All Hallows' Eve Meg (now in eighth grade) and her sister, Sue (now in seventh) embark on a life-and-death adventure on two planes: that of the everyday waking world, and that of some deep dream level that is linked to it in a mysterious and frightening way. . . .

Christmas Eve: Meg is having nightmares in which she is being drawn closer each night to a sinister dark hole. The night she gets there, a hand reaches through the hole and a boy cries out for help. She tries to stay awake, reluctant to go back there. When at last her conscience kicks in and she decides to try to help the boy, Sue provides some unexpected tools to aid in the rescue attempt. In her struggles, Meg meets Morgan le Fay and an ancient mariner named Peter Saltifer. She acquires a virtual ship called Lady Buscarle, in which she aims to fly into the hole.   Meanwhile, on the waking level, the boy - Gavin - is lying in a coma in New York City. In the depths of the Dark World, Gavin is being drawn into a trap laid by the evil Salleman which can end only in Gavin's death.  As Meg races to pull him out she too becomes entangled in the trap and she has to marshal all her wits and ingenuity to try to save them before it is too late.