The novel is thematically a thriller rather than the traditional Golden Age of Detective Fiction murder investigation that features in most of the series.

A small-time confidence trickster on the run stumbles across a sinister organisation, based at a manor house in the Cotswolds, who are using a high-class clinic as a front for their more dishonest activities.

Pursued by his ruthless adversaries, he manages to reach Oxford and stash the stolen formula in the Bodleian Library before he is recaptured.

Coincidentally Appleby is also in the city, called in by his younger sister Jane to find her fiancée, an undergraduate who is gone missing.

What the confidence trickster had thought was an alchemist's operation to produce gold or at the very least forged five pound notes is in fact the development of a brainwashing technique that destroys any sense of human independence or resistance.