Episodes: Series - Line of Duty S1 - 2012

• episode #1
• episode #2
• episode #3
• episode #4
• episode #5

An anti-corruption section investigates a botched counter-terrorism operation. When Steve Arnott is sent to an anti-corruption team, he discovers that his target is the city's top investigator, Tony Gates. To discover Gates' secret, Arnott must participate in a cat-and-mouse game.

After being tricked into covering up Jackie's crime, Gates is despondent over the end of their relationship. As Arnott and Fleming become close to knowing his secret, Gates becomes into an even more dangerous situation.

Gates is attacked by mysterious people. Arnott questions both Jackie and Gates, and Gates tells him that he was in a relationship with Jackie before.

When the money laundering case is transferred to the fight against fraud, Gates is exposed to many threats from unknown persons.

Gates returns to rescue Arnott before he leaves Kate. Arnott confesses to Kate that Gates saved his life. Arnott is confused about Gates, knowing that he is dangerous on the one hand, while on the other hand, he must cooperate with him.