This tense drama reveals writer's storytelling skills
It's a modern dilemma – the bringing together of two families to make a new unit.
Widower Ben (Martin Clunes) and divorcee Rosie (Hermione Norris) are newly married and live in a seaside town with their four teenage children – a girl and a boy each.
They're a busy family, but trying hard to make it all work, despite inevitable tensions with Rosie's ex-husband David (Paul McGann).
Rosie is an anxious mother though and is frantic with worry when daughter Olivia is late home. She might have every reason as the viewer sees the body of a schoolgirl in marshland.
Although it isn't Olivia, she is a schoolfriend and the teenagers are understandably upset by events.
But before long, Rosie's imagination is working overtime. Son Jamie (Alexander Arnold) has inexplicably been washing his clothes; he doesn't have an alibi for the time the girl was killed and, having told his mum that he'd lost his trainers, she finds them under the bed and covered in blood.
She begins to suspect that her son could be responsible for the girl's death and begs ex-husband David to follow Jamie to see what he does, while she gets his computer unlocked to discover lots of pornography.
As her anxiety rises, so the cracks in her marriage begin to show.
Chris Lang's tense drama shows all of the storytelling skills he honed on series like The Bill, Casualty, Soldier Soldier, The Knock, Primeval and Hustle.
The characters are well drawn and the storyline keeps you gripped throughout.
Rosie's suspicion about her son will probably be ill-founded – there is another troubled teenage boy in the home, not to mention the two fathers and (given there was no sexual assault) even the possibility of female perpetrators.
Luckily we only have to wait until tonight to discover the identity of the killer.