Oscar Grimstone works for his Granny in the family business. They're undertakers, so Oscar's grown up around death. But lately Oscar's killing everything he touches. He tries to hide it but it's pretty odd when the grass around you starts to curl and die, or the flowers you're trying to tuck into a corpse's pocket shrivel and turn brown.
Then a shimmering green carriage pulled by ghostly horses pulls up to his house, and a girl ghost -- Sally Cromarty -- identifies him as the source of an astounding amount of phantasma. She refuses to explain anything and leaves, but Oscar isn't giving up so easily. He can't catch the carriage as a living boy, so he becomes -- much to his surprise! -- a ghost and hitches a ride. He scares the Dickens out of dozens along the way and he switches back and forth, from ghost to living boy, violating all sorts of ghostly regulations.
But once he discovers he can become a ghost, and ghosts with unfinished business, like his Dad, may be sticking around, he's determined to figure out who is the ghastly figure that attacked him in his Gran's mortuary and if it relates to the mystery of his Dad's death in any way.