Mum is a celebrated medium--but 13-year-old Cassie, the seventh child of a seventh child, is relieved when she's caught red-handed at a seance and accused of criminal fraud. It means that Cassie is ""ordinary,"" just like slightly older Mary and Tom: the only others of the seven Palmer children still at home. And as much as what mysteriously happens, the interest here is in the forlornness of Mrs. Palmer's spiritualist yearnings and disreputable trade--for her and for the kids. ""A Fine home they had,"" thinks Cassie about to move again, and lose Tom, ""that all the children were so eager to leave and so reluctant to come back to!"" What does happen is that Cassie raises a gruesome, piteous, adhesive ghost: Deverill. (Or is he a crazy tramp? Or a molester of young girls?) And before she does banish him, and free herself, he puts in her way a treasure that will enable the Palmers, cozily, to settle down. The haunting has its enigmas and its terrors; the family story (British, though not obtrusively so) has a rough, fish-and-chips humor and warmth.