Whilst Brian faces disciplinary action for a death in custody from his past the rest of the team discover the gun that killed drug-trafficker Christian Highsmith in 1998. The same gun killed a young boy, Danny Bossano, in 1982 in Gibraltar, a port of call for the ships on which Christian allegedly hid the drugs. The UCOS team go to Gibraltar to meet Superintendent Cruz, the local cold case chief, who believes Danny was part of the dope-smuggling gang. The fact that the gun was army issue also leads to the evasive commander Adam Sinclair whilst Sandra quizzes casino owner Harry Truman, who had been a friend of Christian. Gerry and Steve visit Truman's casino but accidentally get locked in a shipping container whilst shipping agent Gordon Fletcher, an associate of Truman, is found dead.

Gerry and Brian end up on an orange farm from where they hitch a lift with a biker group back to Gibraltar and tell Sandra of the connection between Fletcher and Truman and the fact that Danny Bossano's father Levy met Fletcher just before he died. Levy is tight-lipped as to why he has thirty grand in the house, Truman explaining to Sandra that the thirty grand was actually Fletcher's casino winnings. Meanwhile Gerry and Brian discover that Danny drew many pictures of his friends, the sons of soldiers, one of whom was a young Sinclair, who describes Danny's accidental death. Levy then unmasks Christian's killer who had been paying him to keep quiet. Back home Brian faces his tribunal but Embleton, the man he blames for Anthony Kaye's death in custody, drops charges against him and he is exonerated. However Brian secretly tapes a confession from Embleton as to what really happened and gives the tape to Kaye's mother.

To the annoyance of Gerry, who arrested him for killing his wife sixteen years earlier, Scott Bunce is released from prison when evidence is found to suggest an unsafe conviction. His daughter Lizzie, who saw him standing over the corpse, and the neighbour who saw him leaving the house afterwards are both convinced of his guilt and Lizzie is terrified of seeing him. Then Bunce disappears after a gangster associate of his is severely beaten up. Brian visits his estranged son Mark, who tells him he is about to become a grandfather. They make their peace as Mark helps Brian find proof of Bunce's innocence, leading to the exposure of the real killer. However Brian, after being declared a hero, is told by Strickland he must leave UCOS for giving Sarah Kaye the tape he illegally made of Embleton's confession.

Now dismissed from UCOS Brian is persuaded by Esther to help her friend Margaret Kirby find her brother Peter Sale, who disappeared six years earlier. In the mean time Brian is bothered by journalist Maxine Wilson, whom he believes has been sent by Embleton to discredit him, and needs Strickland's help to get rid of her. Brian visits Jonathan Epstein, jailed for killing his wife Florence for her money, along with his girlfriend Annabel, who seemingly disappeared with the cash. Sale was Epstein's accountant but Epstein does not know his whereabouts and after the visit Brian is attacked. Accompanied by Esther, Brian sets out to find clues to locate Sale, in the process crossing paths with UCOS, who are investigating a con artist with links to Epstein. Eventually Sale is found and, before parting company with UCOS, Brian discovers that somebody is an impostor and Esther has to save him from being killed by them.

UCOS reopen the thirty year old murder of porn king Jim Hockney when his daughter Sara reveals that a DNA test proves she is not his daughter. Her mother Jane cannot provide any answers as she and Jim both had several sex partners. Jim's girlfriend at the time, singer Angela Gold, was charged but acquitted of the murder and now seems to have disappeared. Brian's replacement Dan Griffin arrives, albeit late and is initially treated with hostility by Gerry, who thinks he is a spy. Nonetheless Dan tracks down Angela though in the meantime Sandra learns that Jim's brother Colin sold Jim's porn empire very shortly after his death to his main rival Gavin Reason. Furthermore Jane and Gavin were lovers, Gavin proving to be Sara's father though he was unaware at the time. However it is Gerry's collection of some of Jim's old films, supposedly confiscated by Vice Squad, that identifies the murder weapon and leads to the culprit. The case closed the team watch Angela perform at Ronnie Scott's Jazz Club.

The blood-stained clothes of Simon Belgrade are found in Epping Forest, where he disappeared five years earlier whilst out for a run. Frank Miles, Simon's father-in-law and employer, has a history of violence and his daughter Becky, who was heavily pregnant with Simon's child when he disappeared, seems scared of him. She does not want to believe her husband is dead and nor do his mother Eliza and brother Tim, who portray Simon and Becky as the ideal couple. However Simon's friend Dom and his ex-wife Lois tell the team that Simon and Lois were having an affair, as were Dom and Becky. Simon also had a string of failed businesses behind him and was blackmailing Frank over tax evasion, but with no money taken from his account and no passport it seems unlikely that he skipped the country. An examination of a film showing Dom and Simon's childhood haunts in the forest leads to discovering Simon's fate whilst Dan helps Sandra cope with the anniversary of her father's death.

Following the 1997 General Election Ben Ransley, a young researcher for successful MP Liz Jackson, was murdered and the case is reopened on the discovery of £40,000 in an off-shore account in his name. Ben's best friend, arrogant lobbyist Eddie Trenton, gives Sandra a photo of Ben with his girlfriend, who turns out to be Hana, the Bosnian wife of tycoon Peter Russell, and she also disappeared in 1997. French policeman and former war crimes prosecutor Max Clement comes to London and tracks down Hana, whose whole family was killed in the Bosnian war. Hana believes Ben, with whom she was set to elope, was killed by the man who got her to England and introduced her to Peter but Dan discovers that Ben was in a position to leak information about a government arms deal, which would have been injurious to certain people. This solves the case.

Seventeen years earlier Sandra's first case involved the disappearance, never resolved, of music student Lesley Hewitt and now Lesley's sister Emma has been sent a photo of Lesley walking in a park just before she vanished. Sandra believes that a jogger in the picture was a serial killer responsible for the deaths of other young girls, possibly working with a female accomplice as Emma says that Lesley was offered a gig before she vanished. Ex-model Annie Banks and bookshop owner Stuart McKelvie are also in the photo, taken by Greg Banks, a recently deceased photographer whose studio contains several pictures of women who were abducted and killed. Annie and Stuart initially claim not to know each other but Sandra breaks down their stories and discovers that Annie knows who the jogger is. After concluding the case Sandra leaves UCOS to work with Max Clement.

Fresh from her successful SWAT raid on a group of Russian gangsters DCI Sasha Miller arrives at UCOS to replace Sandra. She is friendly and informal but initially fails to win over Gerry, who misses Sandra. Her first case involves the twenty-five year old murder of Italian Allesandro Manzini, reopened when a knife is found at the allotment he once tended. Massimo, whose son married Allesandro's daughter Giulietta, tells the team that there was anti- Italian feeling on the allotment, especially from two World War Two veterans, whilst lorry driver and druid Ray Barlow is also suspect, having disappeared after the murder. This suspicion is heightened when Giulietta and Ray admit to an affair but Dan's research into wartime Italy changes everything, leading to a confession. Sasha's private life, however, does not run so successfully.

The discrediting of DI Hennessy as corrupt throws into a new light some of his more high profile arrests, including that of crooked businessman Edward Monroe, jailed for killing oncologist Dr Caldwell, whom he blames for the death of his daughter. For Sasha, now alone after discovering her husband's infidelity, the case is painful as she has always believed Monroe murdered her former colleague DC Tyler. As fresh interviews are conducted, it turns out that Caldwell was not a pleasant man and had made enemies of his colleague, Dr Hallerman, passed over for honours; Daniella Yates, director of a cancer charity who was having an affair with Caldwell; and Caldwell's duped wife. However a statement from Grace, a hotel employee of Monroe, throws a more humane light upon the convicted killer, as well as giving Sasha some closure for Tyler's death. Steve, meanwhile finds himself billeting his son Stewie, who has run away from home.