One Step Behind

S1, E3: Three teenagers in 18th century fancy dress are shot dead in a secluded wood on Midsummer’s Eve, and lie undiscovered for two months. As Wallander investigates, it becomes apparent that someone else has already been asking questions. When one of his colleagues is also found dead, it is clear that the cases are connected - but with a photograph of an unknown woman as his only clue, he always seems to be just one step behind.