The team investigate the execution of a reclusive figure and one of his two bodyguards and find a link to witness protection. But the surviving bodyguard is on a mission to find out who killed his friend and the team must find the killer before he does. Meanwhile, Matt and Emma's relationship becomes difficult and Matt refuses to deal with it.

The team investigate the discovery of the decomposed body of Naomi Bancroft nearly two years after her disappearance. Allie takes a personal interest in the case as her former mentor was the lead investigator on the case at the time of Naomi's disappearance. But the new investigation takes a number of twists and turns before it turns up a stalker of Naomi's who may hold a key to her killer. Meanwhile, Matt becomes frustrated at being asked by Emma to give up his job and move to France with her.