A writer of fiction has to strive for plausibility. Tell a true story, though, and the most incredible things become possible.

The Secret (ITV, from 29 April) is a four-part drama about an extraordinary murder, in which a dentist and a nursery school teacher in Coleraine, Northern Ireland, had an affair and then killed their respective spouses so they could start a life together. What made it extraordinary, apart from the cruel mechanics of the plot, was that all four parties, murderers and victims, were devoted members of a local Baptist church. Colin Howell, prior to breaking commandments five and six, was a lay preacher.

This was a gripping, fast-moving account of the story, written by Stuart Urban from a book by Deric Henderson, but it was not subtle. It started with James Nesbitt, as Howell, pounding an acoustic guitar and leading the congregation in a cheerful praise-song. Even then, though, there was something nasty about him. At home, at work, in a prayer meeting, he had an air of discontent at odds with his strenuous piety.