One need not be a Christian to believe in Hell—to be aware, that is, of an irredeemable blackness of soul from which there is no escape, for which there is no consolation. The central character of An Error of Judgement is an agnostic, to all appearances a wise and unusually good man, but he is obsessed by the idea that deep inside he is vile, cruel, and forever damned. Corruptio optimi pessima might have provided Miss Hansford Johnson with one suitable motto for her new novel, though the tortuous and startling series of circumstances she has devised suggest a moral complexity which should challenge most conventional Christian or, indeed, humanist ethical judgments.

William Setter is a distinguished Harley Street consultant married to a big, gay, gadabout wife called Emily. Gradually, through the mild, quizzical eyes of a decent little man called Victor, who somewhat improbably becomes Setter's...