Undercover detectives Liam Ketman (Nick Berry) and Garth O'Hanlon (Stephen Tomkinson) submerge themselves in various dangerous criminal worlds as they go deep undercover to investigate serious crime.
Garth goes undercover as a security consultant to track down the mind behind a powerful vice ring. This results in Liam investigating his old drug-squad colleagues.
Liam's allegiances are tested when it becomes apparent that an old friend is in on the deal. Garth races to find a key witness held captive by two corrupt policemen.
Liam and Garth try to crack a pedophile ring that is operating through a sophisticated website. Liam befriends the webmaster's wife, and Garth goes undercover in prison.
Garth and Liam know the identity of the mastermind behind the pedophile ring, but the problem is getting hard evidence. Liam attempts to get to him through his wife.
Liam infiltrates a white supremacist group that has begun a bombing campaign. Garth is assigned to provide backup to Liam's family, but his presence puts them in danger.
Liam discovers that the leader of the white supremacist group is not whom he seems. An unwelcome visitor from Garth's past mistakenly targets Liam's family.
Liam and Garth pose as drug dealers in a bid to capture Jamie Lamb, the country's biggest cocaine importer. They infiltrate his trusted entourage and fit in so well that, when Lamb's wife leaves him and takes his two daughters with her, he asks Liam and Garth to kill her and bring back proof in exchange for a shipment of cocaine.
Kelly persuades Tania Lamb to help them fake her murder. However, when the "proof" is taken back to Jamie, he turns nasty and ups the stakes, declaring that the deal is not complete until his daughters have been returned to him. Liam and Garth are forced to use Lamb's daughters as insurance to make sure the exchange of drugs takes place. But Tania's fit of guilt leaves Garth and Liam vulnerable.
When DCI Mark Holland is executed in a drive-by shooting, his colleagues suspect local crime kingpin Charlie Pearce of being behind the murder. In order to investigate, Liam, Garth, and Kelly are sent undercover posing as importers of fake watches-and a possible target for Pearce's protection racket.
Garth is in critical condition after being shot by David Pearce. Liam is determined to get revenge, but he must balance his emotions as he tries to find out who was behind the murder of DCI Holland and the attempt on Charlie Pearce's life.
When Fiona Waddington's teenage daughter and young son are kidnapped, a ransom is sent to her family's publishing company. As the kidnappers don't want the police involved, Liam and Garth have to pose as kidnap-and-ransom specialists.
After the botched exchange, Garth is being held by the kidnappers, and Liam is off the case due to concerns over his personal life. The kidnappers send new demands, but Clayton Waddington is unwilling to meet them.
A killer is targeting the members of a dating site. The team work to draw out potential suspects under the guidance of a criminal profiler. Meanwhile, Liam's involvement with an obsessive estate agent causes his relationship with his ex-wife and children to become even more fraught.
Another murder has been committed. Garth is sent undercover to befriend key suspect Grendel. The team become concerned when Dr. Winterbourne works out a pattern to the killings, which suggests that Liam's ex-wife, Pamela, is a potential victim.
Liam returns to duty after the shooting and helps capture crazed armed robber Sean Denning. But when Denning gets out on bail, Liam and Garth must go back undercover.
As Liam and Garth continue to try to gather new evidence against Denning, their task is complicated by a malcontent ex-policeman working with the defense team.
Liam and Garth are called in by the Ministry of Defense to infiltrate a group of disgruntled former undercover soldiers planning a campaign of terror.
The base of the group Liam and Garth are infiltrating has been attacked by ex-IRA men pursuing vengeance. The shoot-out tips Garth over the edge, and Liam must find him.
Liam and Garth are sent undercover to a maximum-security prison as the case against villain Vincent Hunter looks set to collapse.
Garth realizes one of DCI Davies's team is working with Hunter and forms a strategy to identify the culprit before they get to undercover cop Debbie, a key witness.
With the government intending to legalize cannabis, the controversial policy has made Jeremy Church a target, and Liam and Garth are sent to prevent an assassination.
Garth has been released following Dominic's murder and is furious with Liam for failing to back him up. Nicola tries to help her boyfriend with his debt to drug dealers.
Complete episode guide for In Deep with detailed information about every season and episode including air dates, summaries, ratings, and streaming availability in United States.
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