After brilliantly resolving their last case explored in By the Pricking of My Thumbs, Prudence and Colonel Bélisaire Beresford take a well deserved rest in their small chateau overlooking Bourget Lake. Bélisaire is in his element, but Prudence is bored. She wants to set out on new adventures. She dreams of a good fairy who would send them on the tracks of truly dangerous criminals and propel them into mysterious adventures.

It isn’t long before the good fairy arrives in the affectionate form of Babette, Prudence’s Belgian, butterfly-collecting aunt, who witnesses a horrible crime from her train carriage window. A young woman is strangled. Aunt Babette saw the event take place. Despite Bélisaire’s scepticism, Prudence believes her aunt, and this suffices for the young woman to set off to look for the corpse.

To resolve the riddle, Prudence gets herself hired as a cook in a troubling and remote chateau perched high in snow-covered mountains. Here she must employ all her talents as she pretends to be a servant, and resists the advances and plots of the truly strange family composed of an irascible, atrabilious, miserly old man and his four children, each of whom is crazier than the last.

Bélisaire flies to her rescue. Together, without losing their sense of irony or wit, the Beresfords will once again manage to show that “crime”, no matter how Machiavellian, “is their business.”