The first scene is set in 1986. Two men with paedophile tendencies egg each other on to kill an 11 year old girl. One, the slightly less culpable, runs away and makes a new life. 23 years later there is a copycat murder, and this leads to the two men making contact again. The policemen previously involved in the case revisit their investigation. The terrible grief of the newly and previously bereaved parents is explored. Just about everyone in the film, including the murderers, is full of sadness all the time.
I have a theory - I don't suppose it's original - that police procedurals are a dramatisation of our feelings about work, via universalising issues - everyone cares about murder. The particular aspect of working life which is dramatised here is the fact that we must bring our emotions to work with us, to function, but there is no place for them at work. People in this film are embarrassed and shamed by emotions. The more good and authentic people are scruffy and twitchy, and out of step. The retired cop calls on the clever cop, in the middle of the night, and the clever cop is wearing his dead wife's nightie, with a tweed jacket pulled over it. This is not remarked upon. The nightie is his emotion on show, his bereavement.
Very brave of the two actors who play the paedophiles. The small amounts of the film which show their actions are rather circumspect and oblique: some might find it too upsetting to watch, or even exploitative, but I didn't think it was. Terribly sad though.