Dublin, 1816. A young nursemaid conceals a pregnancy and then murders her newborn in the home of the Neshams, a prominent family in a radical Christian sect known as the Brethren. Rumors swirl about the identity of the child’s father, but before an inquest can be held, the maid is found dead after an apparent suicide. When Abigail Lawless, the eighteen-year-old daughter of the city coroner, by chance discovers a message from the maid’s seducer, she sets out to discover the truth.

An only child, Abigail has been raised amid the books and instruments of her father’s grim profession, and he, in turn, indulges her curious and critical mind. Now she must push against the restrictions society places on a girl her age to pursue an increasingly dangerous investigation. Abigail’s searches begin to uncover the well-guarded secrets of two factions—the Christian Brethren and a burgeoning rationalist community—drawing the attention of a sinister figure who emerges in fleeting glimpses and second-hand reports: the man with the lazy eye.