Probably one of the stupidest mystery stories I've seen2/10
Let's first ignore the fact that you have flashbacks from a suspect, and you can't determine if the suspect is really guilty of murder or just covering up for some buddy from his childhood. The chief character is detective constable Thorne who operates on the basis of instincts and is always arguing with his obnoxious, naturally stupid superiors.
Then there are his two subordinates, of which one is a an Asian woman who is a cocaine addict who does lines every chance she gets. The other subordinate is an African-Brit and when they have a free half-hour in the middle of the night, they have a go at some sex. After the sex, he then goes to the bathroom where he finds her doing lines and her response is, "Don't you knock before opening a bathroom door?" That's the end of that scene.
Later that evening she is supposed to be guarding the key witness, who might be a killer (since no one has established clear evidence, but he confesses to killings presumably because he wants protection from his buddy from 10 years ago who might be the killer of women.) She sends another cop who is to help her guard the suspect for coffee, and while he's gone, she ducks into the bathroom for some more coke. She then hears noises coming from the bedroom and is terrified. Since she's not a judo expert, she tries to escape through a window or door, neither of which will open, and whispers into a cellphone for help which does arrive.
Of course, this being Britain, even cops protecting someone from a killer don't carry guns. I guess that, in the UK, when a killer points a gun at a cop, he or she is supposed to do a flying tackle and hope that the criminal drops the gun. At this point, I couldn't stand the stupidity and confusion any longer and shut it off.
I have to say this about this series. First, I'm glad it didn't continue. Secondly, if the police in Britain are this inept and incompetent, crime is bound to soar. How any self-respecting writer or producer could sketch out this storyline is beyond me. Thorne has no more business being the head of a crime unit than the man in the moon and the portrayal is an insult to the police of that country. Ms. Oh's character should have gotten a slap in the face and boot in her butt, but apparently continued on. I couldn't stand to watch this indigestible pap any longer than the scene in the car. I"m not sure why British crime series seem to take such miserably incompetent characters as realistic. Some idea that flawed characters acting out make good television? Wouldn't be too off the base except for the fact I can not in my mind picture any self-respecting police force putting up with these losers. Is this supposed to be realistic? And don't get me wrong, much American television is simply too perfect, but somewhere there has to be a meeting ground. This obviously wasn't it. "Rosemary & Thyme" "Broadchurch" are far better examples of good television.