For Miriam Gardiner, at her engagement party at the London home of her fiancé, Lucius Stourbridge, it should have been one of the happiest days of her life. But, leaving suddenly, Miriam disappears without a trace. Reluctant to cause a scandal, Lucius seeks out William Monk and tells him that the only lead concerns their coachman, Treadwell, who is also missing. Monk, not usually a sentimental man, is moved by Lucius's distress, and assumes that his recent marriage to Hester Latterly is to blame. When Treadwell's murdered body is found, Monk becomes convinced that his death is linked to a terrible secret in Miriam's past that someone, desperate keep it hidden, has killed for, and may well do so again, unless he can stop them.