"One Step Behind" bygger på Henning Mankells roman, "Steget efter".
On Midsummer's Eve, three teenagers dressed in eighteenth-century fancy dress are shot dead in a secluded wood. One of Inspector Kurt Wallander's colleagues turns up dead, someone whose help he hoped to rely on to help solve the crime.
Wallander knows the murders are related. But with his only clue a photograph of a woman no one in Sweden seems to know, he cannot begin to imagine how.
Wallander is locked in a desperate effort to catch the killer before he strikes again. Wallander always seems to be just one step behind.