Disgraced Chappel has been transferred to a desk job following the events of the operation into the paedophile ring, and Vickers has been drafted in to head-up the vice squad as his replacement. When Chappel discovers that Hutchins has disappeared during an undercover operation into a pornographer, he becomes obsessed with finding her. Using his informants, Chappel manages to locate Hutchins, only to see her destroying herself with a powerful addiction to crack cocaine. Risking everything to save her, and under a watchful eye from Vickers, Chappel takes Hutchins to a safe house. But when he discovers that the pornographer raped her, Chappel finds himself up on a murder charge.

Following Vickers' promotion to Chief Inspector, Robinson makes a welcome return to Vice, and on his first day back, he becomes determined to nail a violent pimp, who is involved with the disappearance of two of his girls. As he and rookie Johnstone interview Miles Wilson, the mother of his latest victim is brought in to sit with her daughter during questioning. When she recognises Vickers from their past dealings, she threatens to reveal their lurid past if he doesn't personally deal with her daughter's case. As he persuades Robinson to get both the mother and daughter to testify, Robinson goes to visit Hutchins in rehab, and is stunned to discover that her way of controlling her addiction is to watch punters buying drugs on the street.

The team investigate an amusement arcade manager suspected of recruiting young runaways as rent boys, and PC Adam Parkes is sent undercover in an attempt to gather evidence. While Parkes is drawn into the deep end, Robinson is led on a wild goose chase by one of the boys involved. When Parkes' attempt to trap the prime suspect fails, and the boy whom he is trying to encourage to give evidence starts to ignore him, he suddenly realises that he is being drawn into a whole other ball game. Meanwhile, Morgan becomes jealous when Hutchins returns from rehab and immediately applies for promotion to sergeant. Morgan confides her emotions to Vickers, who suggests that she too should apply for promotion.

The licence of a pole-dancing club is up for renewal, and Robinson is determined to bring down the manageress, who is thought to be running the club as a front for a prostitution racket. Vickers goes undercover to collude with the club's owner, while Parkes and Cole are tasked with being punters for the night. When Johnstone decides to stay-on after hours, she notices Vickers on CCTV returning to the club and taking a woman with him into the toilets. Robinson then becomes suspicious after he appears to be colluding with the chief suspect — and using the club's services for himself. Meanwhile, after being left off the operation, Morgan begins to feel that she's becoming more and more outcast from the team.

Robinson and Morgan are called to the scene of a prostitute found dead in a skip, only to discover that the Serious Crime Group have taken on the case. When DI Delaney requests one of the Vice squad is seconded to his team, Robinson has no reluctance in sending out the ever-increasing problem that is Morgan. As Hutchins' instinct proves to be Vice's key in gathering evidence on the suspect, little does Morgan know that she's out of her depth where her new senior officer is concerned. When he tries to force her to have sex, Morgan realises he has been manipulating her from the start. Robinson is the only one who doesn't fall for her seductive charms, while Delaney is secretly trying to deliberately ruin her career.

While Vickers and Morgan are away from the office on an official home office jaunt, Parkes and Cole go undercover in a club in an attempt to gather information on the owner, suspected of dealing drugs. Parkes realises that their only hope is through the VIP lounge, but upon gaining entry, the pair stumble upon much more than a drugs outfit, and discover that the owner is the ringleader of a human trafficking gang. Parkes tries to rescue a foreign girl, for whom he's developed an interest and becomes involved in the debacle, leading to a stern warning from Robinson. Family man Cole struggles with the undercover lifestyle and comes head-to-head with his wife, who forces him to choose.

Robinson and Cole are trailing a suspect whom they discover has involvement with a major drugs and prostitution racket, but are shocked when they find his boss having dinner with Lorraine. Vickers is desperate to use Johnstone's relationship with the pimp for his own ends when he realises if publicly known, it would have a deleterious impact on Vice, and is determined to sacrifice her while there's still time. As he strikes a deal with the pimp, Robinson unknowingly sends Johnstone undercover to gather information. Meanwhile, Morgan's relationship with Vickers becomes treacherous, and Robinson is quickly catching up. Determined to nail Vickers to the wall, Morgan lodges a sexual harassment complaint.