DS Mary Jane “MJ” Croft and her newly assembled team in the Missing Persons Unit are assigned two separate investigations: the disappearance of a young autistic boy’s mother, and a man who appears to have stolen a large sum of money from his fiancée and subsequently fled. Meanwhile, MJ agrees to appear on the radio to highlight the work of her team and plea for information relating to both cases.

MJ and Jason investigate the disappearance of a young girl following a night out with friends, but they suspect that her own father may have something to do with her disappearance. Amy reopens the investigation into the disappearance of MJ's sister and makes a shocking discovery that brings MJ further heartbreak.

Jason is assaulted by an irate husband whose wife has disappeared, but after DCI Ford intervenes and arrests the man on suspicion of murder, MJ discovers that the missing wife is a “serial missing person,” having disappeared several times before. Amy investigates the disappearance of a witness in a criminal trial.

MJ investigates the disappearance of a lawyer, who seems to have simply vanished whilst playing in the park with his young daughter. Meanwhile, a young woman approaches the team for help in finding her abusive father, whom she hasn't seen since she was 16. Amy stumbles across a phone number registered to MJ's long-lost sister.

Businessman Sam Wise disappears in mysterious circumstances, and MJ's investigation leads her to believe that his financial problems may have been a factor. As Amy interviews a possible witness, she finds herself in unexpected danger. MJ finally comes face to face with her sister.

MJ finds herself stonewalled by DCI Ford whilst trying to investigate the disappearance of a 6-year-old girl who appears to have been abducted by her biological father. Amy tries to reunite a father and son who have drifted apart after the boy came out as gay, while MJ is forced to deal with the reappearance of her father.