Ken and Harry are guarding Upper Ridley Hall, near where Harry lives, and where a big Society wedding will be taking place between Sir Alan and Lady Tessa Bolton's daughter, Kate, and Rupert de Borchgrave, a Belgian Count.

Sir Alan asks Ken to keep a discrete watch on one of his houseguests, Johnny Hunter, a suave gentleman who drives an Austin Healey sports car. Ken senses a tension in the house: why is Hunter nosing around the house and taking such an interest in Kate, and why is Lady Tessa so evasive about him. Why is Kate secretly making furtive phone calls and who is the man who she meets late at night?

While patrolling the grounds, Harry spots two men behaving very suspiciously and stalking one of Sir Alan's stags. He reports this to Philip Braithwaite, Sir Alan's Estate Manager, who doesn't seem to take the matter seriously. Harry suspects that Braithwaite himself might be involved in the stag poaching. He follows one of the estate vans to a ruined chapel which he discovers the