Code of a Killer, review: The true story of DNA profiling grips despite a shaky script

There's only so much the viewer can infer from endless close-ups of test tubes and pipettes

It's all in the genes: John Simm working in tandem with David Threlfall in 'Code of a Killer'

ITV has created a niche for itself in top quality, true crime dramas over recent years, but Code of a Killer, the two-parter that began last night is different from, say, The Widower or Appropriate Adult. For a start, it wasn't written by Jeff Pope. But it's also, ultimately, not the story of the depths of human depravity, but of the height of human ingenuity; how the British geneticist Alec Jeffreys developed DNA profiling techniques now used to solve crimes around the world.

ITV stalwart John Simm played Jeffreys as a slightly neglectful husband and father, who focused only on unravelling the mysteries of the genetic code. Between 1983 and 1986, while he was busy in his University of Leicester lab, another investigation was ongoing, a few miles away in the village of Narborough. Here, DCS David Baker (also a real person) was investigating the murders of two 15-year-old girls, two years apart. By 1986, Baker had a suspect, but he'd need the help of Jeffreys and a pioneering new technique to prove it.

Jeffreys and Baker (David Threlfall) are two TV character cliches working in tandem; the scatty-but-brilliant man of science and the dour-but-determined detective. Threlfall, with his shambling walk and grey mac, inhabited the cliche so beautifully, he was a pleasure to watch. Take note, ITV, here is an actor clearly in search of his own long-running detective series. Sadly, the same couldn't be said of Simm as Jeffreys. It wasn't a bad performance, but Michael Crompton's script never quite got to grips with the science or managed to convey why Jeffrey's discovery was of such huge significance.

There's only so much the viewer can infer from endless close-ups of test tubes and pipettes. As a crime drama, it was on much more confident ground, delivering a cliffhanger that should have you on tenterhooks before next week's conclusion.