Cell-mates Titus Oates and Colly Kibber plan a robbery together whilst they are in prison. However, when they are released, they stage a dramatic fight to give Regan the impression that they have fallen out with each other. Regan trails Kibber, believing that he may have killed Oates, but this is just the diversion the two villains are looking for, leaving Oates to put the criminal plan into place.
Some years earlier Billy Medhurst shot and crippled police sergeant Eddie Jackson before escaping to Spain. Now he is back and Regan is determined to nail him. Haskins advises against making it seem personal since Medhurst has a sharp lawyer to back him up. However, when a meat lorry is robbed, all the evidence points to Medhurst, despite his supposedly being dead, and Regan is eventually justified.
Turkish policeman Captain Shebbeq arrives in England for his old friend Regan to help him track down a gold-smuggling ring, possibly connected to an insurance firm which is fire-bombed. Their joint investigation leads them to uncover another form of smuggling, in the process of which someone puts a bomb in Regan's car. However, he does have the last word on the zealous fellow cop who had him suspended.
Technophobe Regan is initially all at sea when he comes up against the clever computer expert Tony Gray. Gray is bent on revenge against Dennis Longfield, intending to steal his gold bullion consignment with the help of a little computer trickery but, at the end of the day, it's Regan's old-fashioned policing methods that get the results.
Robert Hargreaves, who has an apparently distinguished military background, joins Regan's team. However, at a raid on a caravan site to capture a gang of ex-soldiers who have carried out a violent robbery and are armed, Hargreaves bottles it and cowers behind a tree. Running against the general tide of opinion, Regan believes he is unsuitable for the job but needs to find out more.
Haskins is concerned that, in an adjacent manor, crooks seem to be getting nicked and then released without charge. Posing as an ex-con Regan follows a lead to the Blue Parrot club, haunt of corrupt officers Perraut and Huke who take bribes from villains to let them go and are running a protection racket. Using marked notes he sets them up.
Young Davey Holmes is arrested after an elderly money-lender whom he has visited is attacked and robbed, and May, his mother, asks her old friend Jack Regan to intervene. Although it is proved that he got a legitimate loan and is innocent of robbery, his troubles are far from over as he is being black-mailed and has fallen foul of some very dangerous people. He really needs Regan's help.
Gang boss Joe Castle dies, leaving his ill-gotten gains to long-lost son Steven, who has no criminal connections but seems willing to learn. Regan warns Castle's warring minions not to cause trouble but one of them, Pat Tarley, threatens Steven, saying he wants everything from his father's 'businesses'. The thieves are falling out and Steven cannily plays them off against each other, making Regan's job that much easier.
At a stag party Regan re-encounters well-to-do Raymond Meadows, an ex-criminal who drunkenly admits that his wealth is due to a robbery he once pulled, for which Regan let him go for lack of evidence. Widower Raymond disapproves of his daughter Debbie's boyfriend, flash villain Dougie Owen, and Regan suspects Raymond is using him to get the boy out of the picture. However, Owen plays directly into Regan's - and Raymond's - hands by using Debbie as the innocent pawn in a robbery.
Carter is asked by an old flame, Shirley Glass, to try and help her locate her partner Eddie, who has gone missing. Eventually Eddie, a small time crook, is discovered but he is well and truly dead. Shirley works as a croupier for the smooth Arnold Drake, whom Regan and Haskins suspect of large scale misdemeanours, and they use Shirley and Carter as bait to trap him.
Retired engineer Fred Booth has a very religious but very sick wife and is in need of money. He meets wide boy Artie Ward who pays him to make guns, which Fred genuinely believes to be replicas, but they are in fact the real thing and Artie sells them to kids who use them to hold up small businesses. When an off-duty policeman is killed by one of these faulty guns along with the youth he was chasing Regan is desperate to find the source.
Middle-class housewife Marcia Edmunds approaches Regan in a pub and, in exchange for sex, supplies the names of the gang who recently robbed a bookies - including that of her husband Martin. He is recognized by a witness but has a cast-iron alibi, which Regan is eventually able to break. At the same time he begins to feel that Marcia is using him to get rid of a husband of whom she has long tired.
Violent psychopath Tim Cook, dubbed 'The Leopard' by the press, escapes from custody on a hospital visit, having vowed to get Regan, who put him away. He is sheltered by ex-cellmate Ian Pinder in a house belonging to Pinder's gay uncle but after freaking out and attacking Uncle goes on the run and hides in the woods. Regan and Carter lead the Sweeney in a manhunt which leads to a shoot-out.