Can you justify doing evil to destroy evil? That is one of the dark questions that slowly emerge from the absorbing, unsettling five-part series that begins Touching Evil on 'Mystery'.

Touching Evil has a dashing detective hero, Dave Creegan. But this is no frothy cat-and-mouse game; it is a collection of twisted contemporary tales in which Creegan, part of a team of high powered London detectives, comes face to face with unspeakable killers. It would be easy to guess that Touching Evil was created and largely written by Paul Abbot, who invented the great, personally flawed, crime solving psychologist of Cracker. In the mould of the most intriguing modern crime solvers, Creegan has psychological turmoil of his own, and his cases have more to do with confronting the criminal mind than with hunting down evidence.

Robson Green, who plays Creegan, has piercing blue eyes, slightly thinning hair and a taciturn quality that causes his partner, Susan Taylor, to ask if he has spent a lot of time alone lately. He has; he is recently divorced, the father of two small daughters, and quietly torn apart over it. He also has a conspicuous scar on his temple. Touching Evil unfolds with such deliberation (too much in the slow going early stages) that it takes a while to learn that the scar is the result of a bullet to his head, taken during a not so distant investigation. Creegan may be brave and smart, but he's not infallible (the better to worry when he seems in danger).

The series follows three separate cases. In the first episode Creegan joins the fictional OSC, the Organised and Serial Crime unit, and tackles the most disturbing case of all. Three small boys have been kidnapped. The clues - a buried sneaker and a plastic daffodil left at the scene - lead to a cool, professional geneticist named Hinks, who they suspect has kidnapped and murdered children before. If his pattern holds, the detectives have six days to find the boys before they are killed.

Of course, as the renegade hero, Creegan is willing to break the rules to save the children. But it is the unfolding of his character that becomes most fascinating to watch as Mr. Green smoothly allows us to see the tension between Creegan's normal life as a father and professional, and the flashes of dark intuition that help him track the killers. (In a more outgoing mood, Mr Green played the young doctor obsessively in love with the middle-aged Francesca Annis in the quirky 'Masterpiece Theatre' romance Reckless, also written by Mr. Abbot). If Creegan ever takes on the complexity of Robbie Coltrane's Fitz in Cracker, he has an enigmatic allure that grows through the series.

The next stories feature similarly monstrous crimes. In the second, several patients are drugged and killed in a hospital - in what appears to be unsolicited euthanasia. The third has the least interesting crime, involving the Internet, college students and mutilated corpses. But it offers the most satisfying glimpses into the lives of the detectives. All are played with a crispness that suits the series, especially Ms. Walker. With her cropped hair and brisk manner, she brings an echo of Jane Tennison from Prime Suspect to the role of Creegan's no nonsense partner. This precision exists in a world often filmed to look ominously claustrophobic.

Though each case is self-contained, there are threads that go through subsequent episodes, and the question left dangling at the end of one episode leads to the startling conclusion of the next instalment. Another murder is solved but that solution only raises more questions of ethics and morality. This psychologically chilling series takes on the big issues beneath all detective stories: life and death, good and bad, the extremes to which humans go. Among it's other qualities, Touching Evil is perfectly named.