Obsession is a book and a half. From the afterword I learned that the title was forced on the story by the publisher and Ramsey Campbell wanted "For The Rest of Their Lives". While Campbell's preferred title would have grabbed me more quickly, I do think "Obsession" suits the story, which deals with the destructive power of an obsessive idea - that having wished for an received something four children would spend the rest of their lives repaying, well at least in the case of one of the four.
<spoiler>Peter is a hero when he saves his grandmother's life, but when she moves in with him and his parents life becomes difficult for all of them. He wishes she would leave, and she does so by dying. The guilt he carries poisons his adult life and drives him to do terrible things.</spoiler>
It's powerful stuff and the clever twist makes it tragic. So much is lost and so little gained for a moment's breathing space. The maxim "Be careful what you wish for" has never been more apropos.
I read this as part of Halloween Bingo. Assuming it is called the planned square is SMALL TOWN HORROR.