The team investigate the murder of an East German immigrant, but they only have his mysterious final words to work with. As they attempt to piece together his remarkable story, Sandra attempts to gain the trust of his estranged daughter.

Thirty years ago, Strickland and a group of his associates, including Stephen Fisher, were involved in a covert operation on behalf of MI5. Now, someone is trying to kill all the members of that group and Strickland turns to the UCOS team for help.

Lane's future at UCOS is threatened by a death in custody which emerges from his past. Meanwhile, the discovery of a mysterious gun in the Thames re-opens the unsolved 1998 murder of a playboy shipping heir and leads the team to the Rock of Gibraltar.

The team unlock over three decades of secrets and lies on the Rock of Gibraltar and find the link which solves the murder of a playboy shipping heir from '98 and a young local boy from '82. With both cases solved, they return to England where Lane faces a disciplinary hearing, dragging up a death in custody from his past which threatens his career in UCOS.

Family ties affect both Gerry Standing and Sasha Miller. While Sasha is forced to work with ex-husband Ned as he fills in for Strickland, Gerry returns to his roots in Bermondsey to help arrange his daughter's wedding. As a consequence he is thrown into a case involving the possible murder of an architecture student who is also the grandson of an old friend.

Meanwhile, Danny Griffin has been on an FBI course in reading body language.

A mix tape from 1983 is discovered, containing the voice of a teenage girl who was murdered shortly after it went into her school's time capsule. Griffin becomes convinced that the girl is reading from a speech secretly prepared for the Queen to broadcast in the event of a nuclear war.

Meanwhile Sasha is distracted by a romantic entanglement with a charming record shop owner and Gerry is dreading his future son-in-law Robin's stag night, which promises to be something very special...