This was Canning's first play for radio, broadcast by BBC Radio 4 on 12 August 1981, repeated on 11 May 1983 in the Afternoon Theatre series. Diana and Martin Stone were played by Rosalind Shanks and Sean Barrett.
Young Billy, staying with his Uncle Martin and Aunt Diana, goes bird-watching but takes some pictures of a couple having sex in a car. Diana and Martin recognise the couple; one is Martin's employer. Of course they wouldn't dream of using the pictures to get Martin a promotion. Or would they?
This is a rather different and more amiable kind of blackmail from that shown in Canning's 1963 novel The Scorpio Letters, and Diana's true motivation is held back until the final scene.