In the winter of 1920, Mary Russell is on the cusp of turning 21 and lives a double life of Oxford University theological scholar as well as a consulting detective and partner of Sherlock Holmes.

After events in The Beekeeper's Apprentice, both Holmes and Russell are aware that their relationship and partnership has changed, perhaps romantically, but neither is eager to broach the subject.

A chance encounter unites Russell with Veronica Beaconsfield, an old Oxford acquaintance who is worried about her former fiancé, Miles Fitzwarren, a returned soldier and drug addict.

Veronica introduces Russell to the well-financed New Temple in God and its leader, the enigmatic, charismatic Margery Childe, who preaches empowerment of women.

When an attempt is made on Veronica's life, Holmes and Russell discover a mysterious pattern of deaths where fairly wealthy women have left large bequests to the Temple.

Against the effects of the drug and solitary confinement, Russell struggles to retain her identity and will to survive, and in the face of possible death, contemplates her love for Holmes.

In an author interview, Laurie R. King is noted to describe herself as a "...feminist-although that basically means I support the right of a woman to get paid for doing the same job as a man, not that I believe men to be inferior or superfluous."