Elderly dementia sufferer Nancy leaves her care home to report that her policeman husband Jimmy, who disappeared in 1956 was actually murdered. Harry Page, an old friend of the couple, reports that Jimmy had gambling debts and got into a fight the night that he died. Sasha takes Nancy back to her old house where she recalls Jimmy's violence and jealousy. A grim secret is discovered in the bedroom wall, in turn leading to the solution of the murder. Meanwhile Steve is called to the police station when his son Stewie is cautioned for minor drug possession, which brings him into conflict with his ex-wife Tricia. They do not part on good terms.

The team notice that DNA from teen-aged market trader Spencer Rogers, arrested for throwing a brick on the motorway, matches that of interpreter and chess club member Agnes Bradley, murdered in 2010 and when Spencer's mother Kelli tells Sasha that Spencer was the result of her being raped by an unknown man it is apparent the rapist is the murderer. Suspects include Jeremy Powell, who, according to chess club captain Viktor Proust, smarted because he could never beat Agnes and Chilean diplomat Carlos Alvarez who had Agnes black-listed after one of her translations warned students against his womanizing. Whilst the rest of the team is busy trying to catch the murderer Steve is occupied with bringing his hate-filled dying father Robbie to a hospice in London.