The previous book's adventure in Herefordshire left the protagonist Peter Grant deeply involved in a relationship with Beverley Brook, the resourceful young woman who had saved him from captivity by the Faerie Queen.

Also involved is the renegade policewoman Lesley May – once Peter Grant's valued colleague witch he greatly cared for, now The Faceless Man's cunning and highly resourceful accomplice.

However, though the Faceless Man is clever and ruthless, he lacks combat experience, while Nightingale is a veteran of deadly battles against Nazi German wizards in the Second World War – enabling him to survive all traps and relentlessly pursue his foe.

In the aftermath, Newton's famed Third Principia had fallen into the hands of Lady Helena Linden-Limmer – and Nightingale is content to leave her the task of deciphering its obscure Latin.

However, Lady Ty invites him to a stern talk, to warn of the dangers and dilemmas inherent in a mortal man loving an immortal goddess (and vice versa).