Everyone knew about the kind of films they showed at the Calliope Club, once the Residents' Association and the local Women's Group had given them some free publicity.

But when Peter Pascoe's dentist suggests that one film in particular is more than just good clean dirty fun, the inspector begins to make a few discreet inquiries. Before they bear fruit, though, the dentist has been accused of having sex with an underage patient, the cinema has been wrecked and its elderly owner murdered.

Superintendent Dalziel expects no more from professional men who watch blue films. But Pascoe has a hunch that this time Dalziel is way off target.