When you hear that this murder mystery is set in a sleepy seaside town, you may be picturing a gentle British detective series along the lines of "Midsomer Murders". But "Broadchurch" is bleak. It takes you to uncomfortable places, exploring the effects of a major crime on a tight-knit community, as two detectives (David Tennant and Olivia Colman) investigate the death of a local boy. A further two seasons widened the net, introducing other characters in the town (and new crimes).