Season 4 - Episode Guide

The team investigate when a father stages a protest in an attempt to persuade the army into opening a search for his missing son, who has disappeared since returning from a tour of Afghanistan. Initial suspicion falls on three of his army colleagues who he was drinking with on the night he disappeared, but when one of them is involved in a hit-and-run, the team discover that a secret affair was taking place within the confines of the regiment. With none of the suspects willing to grass on their comrades, the team lead a manhunt for a missing satellite navigation system, which could lead them to the location where they suspect the missing man's body has been buried.

When convicted killer Dean Price is found dumped on wasteground, having been attacked in the same way as his victim, Alex Wojnar, the team realise that they may be dealing with a case of revenge. Wojnar's sister becomes the initial suspect for the attack, but when the team uncover Price's phone in his brother's house, they realise that Price may not have been guilty of murder. When DNA evidence reveals that Wojnar's sister's husband was present at the scene of his murder, family loyalties become divided, and following some frank confessions, the team soon uncover that Price's nephew may have been responsible for the attack of which his uncle was sentenced.

The team investigate when a local community leader is shot outside the boxing club which he runs for disadvantaged youths.

When an elderly widow is brutally attacked in her own home on a notorious London estate, the team set out to find her attacker.