The Secret (ITV, 9pm)

IN 1991, 31-year-old Lesley Howell, a former nurse, and 32-year-old Trevor Buchanan, a policeman in the Royal Ulster Constabulary, were found dead in a car full of carbon monoxide in a garage in the seaside town of Castlerock, Londonderry. Suicide was the verdict because their respective partners – dentist Colin Howell and Hazel Buchanan – had been having an affair.

But, in addition, to the lovers failing to establish a relationship, it took another 20 years for Colin Howell to confess to double murder, implicating Hazel Buchanan. Playing the man who became known as the Driller Killer was an eerie choice for James Nesbitt because he came from the same Northern Ireland community, Coleraine, as Howell.

“My sister was at Lesley Howell’s coffee mornings. Two of my best friends were patients of Colin’s. When Colin dumped the bodies in his father-in-law’s garage and ran along the beach, he went right past my parents’ house, where they were sleeping. I found that quite scary,” 51-year-old Nesbitt told Radio Times.

Howell went on to have five children with his second wife – having fathered four with Lesley – and was a Baptist church Sunday school teacher. Nesbitt came from a Presbyterian background and recalls singing hymns around the piano on Sunday nights. He thinks carefully before explaining how he found a way to enter the dark world of Colin Howell.

“Religion was important to him, but his self-belief meant he felt that rules didn’t apply to him. In the real-life stories I’ve done, I’ve seen wickedness and loss and menace and terrible acts of violence and cruelty. But I have also seen some amazing generosity and spirit and love. So, generally, I’m optimistic about masculinity. As a father of daughters you want to be. Though, in a way, it’s easy for me to be optimistic. I’m in a pretty good position,” says Nesbitt.

In the case of the killers, Howell faces another 20 years in prison while his accomplice, who has failed to have her convictions overturned, will not see freedom until 2029. The four-part drama is based on a best-selling book by veteran reporter Deric Henderson, the former Ireland Editor of the Press Association.

The drama has all the hallmarks of a major success - not only does it have a gripping and disturbing story at its heart, the screenplay has been penned by Bafta-winner Stuart Urban, whose previous works include the hugely acclaimed Falklands war drama An Ungentlemanly Act.

At one point Nesbitt seemed a comedy-drama stalwart, but showed he had heavyweight potential by starring in Bloody Sunday and then Murphy's Law, Jekyll, The Passion and Five Minutes of Heaven. More recently, he's appeared in Monroe and Peter Jackson's three-part movie adaptation of The Hobbit, and the BBC's acclaimed The Missing. His next project is returning as Adam in Cold Feet, a revival of the series that made him a star.

Boomers (BBC1, 9.30pm)

THE three couple gather for the rapidly arranged wedding of Maureen's mother Joan, whose new husband-to-be Roy is 20 years younger than her. However, after an impromptu stag do, the morning of the wedding sees Roy missing. The boys gain access to his room and find the groom, naked, apparently dead on the bed, and a semi-clothed maid emerging from the bathroom. June Whitfield guest stars, with Philip Jackson, Alison Steadman, Russ Abbot, Stephanie Beacham, Paula Wilcox and James Smith. Last in the series.

Witless (BBC1, 11.25pm)

NEW series. Comedy about two flatmates whose lives are thrown into disarray after witnessing a gangland shooting. They are whisked into witness protection, given new identities and left to fend for themselves in a grubby flat in Swindon. Leanne leaps at the chance to create an extravagant alter-ego, while Rhona wishes to get back to her old life. After Leanne's 'acting' threatens to blow their cover, Rhona decides to take matters into her own hands. Kerry Howard and Zoe Boyle star, while sports presenter John Inverdale appears as himself.

Viv Hardwick