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.