A groom is killed at his bachelor party, and the man who reports the crime is the ex-husband of the bride. The detectives race to find the missing 18-year-old best man, who may have been the killer or another victim.

A man is found murdered on his houseboat, but the woman who alerted police has fled the scene. When Vivienne and Billie question the victim's widow, they discover he was having an affair with his best friend's wife.

When the body of a woman turns up by the river, the detectives track a suspect through a dating site, only to find he may have shot himself. While Rob and Vivienne disagree about whether it was a murder-suicide, Billie worries about Amber, a witness in another case.

With Billie stabbed and her attacker on the loose, Vivienne blames herself for not recognizing that Billie was in danger. As the team scrambles to track down Amber, they discover that there's more to her than meets the eye.