Still affected by the death of one of their team, Ronnie and Joe have a new case to deal with when a young mother is stabbed to death in a busy London marketplace.
When a spate of shootings claims one of Ronnie and Joe's own, Wes Leyton, the pair are left with a race against time as the next target the shooter has in his cross-hairs is CPS boss Henry Sharpe.
Maids find blood-stained sheets but no body in a hotel room, booked with a credit card stolen from businessman Charles Hutton by Rufus Barton, a school classmate and secret lover of Hutton's daughter Georgia.
The body of elderly businesswoman Ranya Habib is found at a suicide spot but foul play is suspected after a neighbour tells Ronnie he heard her arguing with somebody.
Unemployed family man Neil Lester is battered to death with a paper-weight in his own home, having convinced his wife that he has been working for the past nine months
When a car is pulled from a river with a skeleton in its boot the pathologist reckons both have been there for a quarter of a century and eventually the dead man is shown to be Taylor Kane, one of the first black undercover officers, who disappeared at the time of the Brixton riots.