Deceit review: A gripping portrayal of a real-life undercover operation

In July 1992, Rachel Nickell was walking with her toddler son in a secluded section of Wimbledon Common when she was attacked by a stranger. He stabbed her 49 times, sexually assaulted her, and left her for dead, her little son – the only witness – clinging to her lifeless body.

It was inexplicable, and unusual, in that in such cases those involved are usually at least acquainted with one another. The officers investigating it said they had never seen such a thing before. Rachel was young, blonde, pretty, a model – and the very model of the kind of victim the tabloid press seize upon. The brutal murder shocked the nation, as the headline writers said, and the pressure on the police to find the killer was intense. That, indeed, was the real problem, as Channel 4’s drama Deceit, based on real events but with shall we say creative flourishes, demonstrates.

The police turned to the then newly trendy practice of psychological profiling to come up with an idea of the man they were after. Having done that, they picked out a promising young female officer to engage in what was later called a “honey trap” scheme to catch their main suspect, Colin Stagg.

Stagg is played with just the right mix of sinister and awkward by Sion Daniel Young. He is the local weirdo who the neighbours have phoned in about, and the police think he did it but only have circumstantial evidence. Niamh Algar, who turned in such a powerful performance in The Virtues a couple of years ago, plays undercover officer Sadie Byrne, the “honey trap”, pretending to be Lizzie James.

Byrne is ordered to contact Stagg by letter and befriend him, or more, by suggesting that she’s into the same type of violent sexual fantasies he enjoys. She is plucked from her usual role as an effective and brave agent catching violent yardies and sent in to flirt with a man the police have reason to believe is capable of stabbing her to death. Presumably the officer in the real case felt the same sense of tension that Algar exudes so well. Harry Treadaway is also highly believable as DI Keith Pedder, a perfectly good copper, determined to get Stagg, but maybe a little out of his depth.

As so often, however, the show is stolen by the ever-watchable Eddie Marsan as the the psychologist Paul Britton, a man the police are perhaps overly dependent on. He speaks with the considered precision of a high court judge, stressing to Byrne that her job is to “make Stagg fall in love with you”, but also “never put words in his mouth or ideas in his head”. Somehow Marsan makes this presumably normal academic seem more creepy than Stagg. When he makes Byrne a cup of tea, the dialogue and editing are enough to suggest to us that he’s laced it with Rohypnol. It’s deeply unnerving.

Deceit is a gripping portrayal of at least a version of what happened, and what went wrong. The Nickell murder is so long ago that this part-dramatisation of events qualifies as a period drama, with the appropriate touches – people smoking freely in offices, VHS tapes, old cars. It is a reminder that flawed investigations are nothing new. It is rema rkable that so many big notorious cases that grab the attention so often result in the police trying to fit the facts to their favoured suspects: Jill Dando, the Yorkshire Ripper, the Birmingham Six, John Christie…

I’d like to see a psychologist analyse why the police so often get it most wrong when everyone’s watching them.