With Robinson's increasing aggression and temperament, it seems to paint him the prime suspect. However, Chappel believes otherwise and sets out to find the real killer.

Chappel assigns Joe Robinson to the case, unaware that the girl is actually harbouring feelings for Robinson. When his wife Shirley becomes suspicious of his interactions with the girl, Robinson finds his marriage on the rocks and the impending pressures of the job becoming too much. Chappel is forced to find new evidence after the girl reveals that she's pregnant and no longer willing to testify.

When the team raid a brothel operating as a massage parlour, they discover that the young female employees have been smuggled into the country from Eastern European refugee camps. One girl offers to testify against the ringleader, but only if she is given round-the-clock protection.

Tasked with investigating an illegal gambling and prostitution ring operating out of a pub, Chappel and Hutchins posing as thrillseekers. However, after Chappel nearly blows his cover, he's shocked to discover that the haunt is frequented by former Vice officer Dougie Raymond.

Chappel goes undercover as an insurance-broking lodger to investigate a suspected porn merchant, who makes a sideline in dirty movies whilst running his own above-board video rental shop. However, when he learns that the residence is in fact the base for a paedophile ring, the case is recategorised and taken from Vice, leaving Chappel furious upon discovering that the case has been handed to Robinson – his first assignment since his promotion to Inspector. Meanwhile, as Hutchins begins questioning her loyalty to Chappel, the latter—unable to continue allowing the repeated abuse of a 12-year-old girl—attacks the prime suspect, eliminating any chance of bringing down the ring.

Chappel hopes to resume his relationship with Jane despite her descent into prostitution, but his plans are threatened when Vickers begins sniffing around. The team are visited by DC Damon Hills, who informs Chappel that he suspects Vickers of being bent, and wants to bring him down by whatever means possible. Using Hills, Chappel sets up a secret sting operation, soon realising that not only is he being double-crossed but Vickers has sent Hills to trap him. Determined to give his enemy the treatment he deserves, with Jane's help, he invents a fake, but believable, rape claim in order to ensure that Vickers goes down for as long as the law will allow.

When Raymond falls hopelessly in love, he attempts to woo the one particular girl into a real relationship, instead of a business arrangement. However, when she subsequently leaves the country to traffic drugs, Raymond goes on the rampage and jeopardises the entire case... and his career in Vice.

Chappel begins to use Raymond's connections as a means of gathering evidence, but when Dougie's level of enthusiasm – and hope that his efforts may win him his job back – backfire, Chappel's reliance is left in tatters.

DI Pat Chappel finds himself involved in a turf war between two rival pimps when he investigates the murder of a prostitute. Whilst gathering evidence against his prime suspect, he takes the high-class Nikki under his wing and learns that her pimp is physically abusive towards her.

Chappel resolves to help Nikki after she refuses to give a statement to the police, and gets personally involved trying to protect her from Hinkley, ostensibly, a respectable family man. Less than pleased at the attention he's receiving, Hinkley needs Chappel's help when his own daughter is kidnapped by a rival pimp.

Chappel's former boss Frank Vickers is found lurking in the basement during a raid on a Soho brothel, and the team learn that Chappel has a more-than-shady past involving former prostitute Jane Farrell, with whom he fell in love. Vickers is determined to clear his name, and Chappel's life looks set to be blown apart when Vickers reveals some very sordid secrets to his colleagues in Vice. Chappel goes in search of Jane, and discovers that one of her friends, whom he was friendly with, disappeared some years previously and has never been found. When Chappel finds the body in the basement of the brothel, he becomes determined to prove Vickers' involvement in her death.

Attending the trial of a prostitute accused of murdering her pimp, Chappel tries a little gentle persuasion in an attempt to get the prosecuting barrister to press harder to gain a conviction, unaware of his own personal troubles. When the barrister is caught with a prostitute in a car park by Cheryl and Kirsty, he uses the excuse that he is 'gathering first-hand research' for Chappel and is let off with a caution. However, when caught again, Chappel realises he's unleashed a more dangerous beast than he ever could have realised. Meanwhile, Joe and Kirsty start to develop an explosive relationship, and when Jane loses her new job and goes back on the game, Chappel soon has new problems.

WPC Cheryl Hutchins takes on more than she can handle while undercover, when she discovers that a nightclub boss has a side hustle in S&M films. This also brings back painful memories to Chappel.

Hutchins is making slow progress in her bid to find the young boy involved in a porn film, but believes his parents are hiding important information about his past. Meanwhile, Chappel's professional relationship with Dr Weir becomes personal.