It is summer 1963, the era of The Beatles and the first James Bond movies. Youth culture is taking over, but the shadows of the Second World War and its demon offspring, the Cold War, still loom, particularly for the older generation. Nowhere is immune to the mood of paranoia, not even the tiny east Hertfordshire village of Fordham Market, where skullduggery, with its roots in both conflicts, is afoot.

Through a series of unexpected fatalities, Richard Warren, a well-educated, gay man in his mid-thirties, has inherited not only The Priory, his parents' impressive pile in Fordham Market, but also Wyvern Hall, his uncle's neighbouring, slightly more ramshackle, estate. The only problem is that Richard is broke and his dead relatives seem only to have bequeathed him debt. The obvious solution would be to sell his uncle's estate, which would at least enable him to deal with the debt secured on The Priory. Unfortunately, Richard discovers that shortly before he died, his uncle amended his will to grant a lifetime interest in Wyvern Hall to his longtime assistant, Neville Smith, better known as Nippy, the effect of which means that Richard will be unable to sell Wyvern Hall until Nippy dies.

Richard is helped out of this jam by his old Cambridge friend, Tony Smallwood, who encourages him to locate and suppress the known copies of the amended will, so that the only will available for probate is the original unamended will held by a local firm of solicitors. But Smallwood's apparently disinterested assistance in this piece of sharp practice conceals an ulterior motive. He is a double agent working for the Soviet Union. Cuthbert, Richard's uncle, also used to work for MI5 and in his retirement, reviewing transcripts of old cables, uncovered a network of Soviet agents at the heart of British intelligence, headed by the shadowy figure of a double agent bearing the codename Nightshade. News of this has reached Moscow, and Smallwood has been ordered to locate and destroy Cuthbert's research, which his Soviet handlers have codenamed the Mother Goose dossier.

The mission ought to be straightforward, but the unwitting intervention of several Fordham locals complicates things. The reason for Nippy's determination to remain at Wyvern Hall is so that he can continue work on the perpetual motion machine. His allies in this endeavour are Peter Marshall, a London teenager staying with his great-aunt, Flo Hodges, and his girlfriend, Terri Hammond, daughter of the local butcher. It is apparent to the teenagers that Richard Warren and Smallwood up to no good. They overhear them talking about a copy of an amended will located somewhere in Wyvern Hall. The teenagers resolve to find this document, which they hope will support Nippy's case. But what Peter and Terri do not realise is that Richard is not comfortable with Smallwood's plan. He feels that he is being rushed into selling Wyvern Hall, but he sees no alternative, if he is to preserve his ownership of The Priory. Unexpectedly, he is rescued from this dilemma by the arrival of Agatha Ponsonby, a childhood friend.

Agatha is a brisk, no-nonsense person and although also gay, proposes, much to Richard's surprise, that he and she get married. She tells him that she is the potential beneficiary of a family trust, but only if she marries and produces a child. Richard is fond of Agatha, and access to substantial funds is not to be sniffed at, but the idea of marriage and procreation troubles him. Agatha, however, makes it clear that the arrangement will not preclude the partners in the marriage from indulging in the occasional liaison more in tune with their respective sexual orientations.

The divergent aims of the protagonists soon intersect in unexpected ways and set in motion a chain of events leading to a dramatic denouement. In the process the identity of Nightshade is revealed. But at the end doubts remain whether Nightshade really has been identified.