A police raid ends disastrously when intended target Billy Coates dies in custody. A threatened riot is quelled by a rousing speech from high-flying black officer John Othello.

After announcing an initiative to promote more black and Asian police officers, Metropolitan Police Commissioner Sinclair Carver is forced to resign after a private racist remark to his deputy Ben Jago is recorded by a journalist.

On the day of Othello's marriage to his girlfriend Dessie, he is summoned to Downing Street and offered Carver's job. The Prime Minister allays Othello's fears that this is a token gesture.

Jago warmly congratulates Othello, and readily agrees to be his right-hand man - hiding his bitter jealousy. In private, he begins plotting Othello's downfall by seducing Dessie's best friend Lulu.

Othello's first public statement is to promise an inquiry into Billy Coates' death. In private, Jago says that he thinks it's a pity that someone as worthless as Coates should threaten officers' careers. Othello replies that it's a matter of principle, and from now on there will be zero tolerance for racism.

Lulu confesses her promiscuous past to Jago. Excited, he asks if Dessie was the same, and is visibly disappointed to be told the opposite. Later, he anonymously posts racist messages about Dessie on a white supremacist website.

Dessie is threatened by racists while jogging and has a brick through her window. Othello orders Jago to give her police protection, and Michael Cass is assigned to the job. He and Dessie have mutual interests.

The Billy Coates inquiry starts poorly, with the officers stonewalling with the same story. Afterwards, Othello questions Jago's commitment and says that he needs a result. PC Alan Roderick reveals a longstanding feud between Coates and PC Adey, and claims that Adey over-reacted. Delighted, Othello makes Roderick the key prosecution witness.

Othello tells Jago that he is so obsessed with Dessie that he's literally terrified of losing her. Jago reassures him - but sows the seeds of doubt by revealing Cass' womanising reputation. But this shouldn't affect Dessie - after all, she's put her wild times behind her.

Returning home, Othello finds Dessie and Cass sharing a joke. He later quizzes her about her past and asks why she gets on so well with Cass. She asks if he's jealous, and he wonders aloud whether he should be. Later, Jago tells Cass that Othello's marriage is a sham.

Alan Roderick is ostracised by his fellow officers. Jago asks him if he feels up to it, saying that it's not the court appearance that's a problem, it's what happens afterwards. The next day, the trial collapses after Roderick kills himself.

Dessie and Cass celebrate the latter's birthday, and he makes a pass at her, which is rebuffed. Later, he spills wine on his shirt and Dessie hands him Othello's robe while she washes it off. Othello returns home to discover a very suspicious scene. After Cass leaves, Dessie tries to mollify him, but to no avail.

Jago offers to have the robe analysed for "secretions" and suggests an evening out to calm things down. This begins well, but tension arises when Cass joins them, at Dessie's invitation. He claims that someone has been telling lies about him, but Othello threatens to kill him. Jago restrains him, and suggests Cass leaves.

Back in the flat, Othello demands to know who Dessie has slept with since they met. Terrified, she goes to Lulu's. Othello obsessively sorts through her things, looking for "evidence". He attacks Cass in a car park and dries up during a live television debate. The media claims he's cracking up.

Jago tells Othello that the lab report was positive. Enraged, Othello returns home and confronts Dessie. She denies everything, and he smothers her with a pillow.

Lulu and Jago break into the flat and discover Dessie dead and Othello distraught. Jago claims he was coming to tell him that the lab report was inaccurate - it proves Dessie's innocence. Othello orders Jago and Lulu out, picks up a gun and kills himself.

The Prime Minister agrees that Othello's promotion was an over-ambitious experiment that failed, and decides his replacement should be a safe pair of hands - Ben Jago.