A skeleton found in the cellar of a building being demolished prompts investigation from DCI Cassie Stuart and her colleague DS Sunny Khan into the murder of a young man that could potentially span back thousands of years. Discovery of what they believe to be a car key near the body not only dates it to within the last 65 years, but also leads them on a trail in the hope of identifying the victim. At the end of the trail is a diary belonging to Jimmy Sullivan, a young man missing since 1976 who appears to be the victim. The final pages of the diary contain several names and addresses, amongst them are Beth, Father Rob, Frankie C and Mr. Slater. Four seemingly unconnected people living very separate lives. It is now down to Cassie and Sunny to find out what happened to Jimmy and to finally get him home.

Having identified the body in the cellar as Jimmy Sullivan, Cassie visits the victim's mother, who is relieved that she might finally find out what happened to her son 39 years after he went missing. The detectives focus their investigation on the names in Jimmy's diary, who are revealed to be a government advisor, a priest, a retired bookkeeper and a housewife with a secret past. What part, if any, could these four wildly different people have played in Jimmy's disappearance and demise?

Cassie and Sunny dig deeper into the lives of two of the people mentioned in the diary. They begin with Father Robert Greaves, who remembers Jimmy fondly, but is unable to help identify the mysterious 'Jo-Jo', the person who it appears gave Jimmy the journal. The detectives also meet Eric Slater, the former bookkeeper to Arlingham House. He also remembers the victim well - but can he provide any clues to his disappearance?

As the investigation into the cold-case murder continues, the forensic team discovers that the marks on the victim's body are consistent with known gangland torture methods. With this in mind, Cassie and Sunny question Sir Phillip about his involvement with a prominent East End crime family 40 years ago. Did the businessman or any of the shady associates of his youth have anything to do with Jimmy's disappearance or murder? Meanwhile, Eric and Claire's anniversary gets under way.

As Cassie and Sunny continue their investigation into the cold-case murder, the net tightens around the people whose names were found in the victim's diary. Sir Phillip Cross makes a difficult decision to salvage what is left of his reputation while at the same time protecting his family, Father Robert comes clean to the police and Ray returns home to find Lizzie gone.

Father Robert's revelations prove to have lasting repercussions, especially for Caroline when she goes into premature labour. Bella and Josh deliberate over the best way to deal with their father, the search for Lizzie continues and Maureen is finally able to lay Jimmy to rest.