DCI John Luther and his partner DS Justin Ripley participate in a dramatic takedown of two suspects inside a burning warehouse. Luther later returns home.
A woman named Emily Hammond returns to her flat where she lives alone. She sits on the edge of her bed and takes off her shoes them climbs into bed to go to sleep. Once her eyes are closed a man silently emerges from underneath her bed and stands over her, holding a wig. Emily's eyes open.
The next day Luther and Ripley respond to Emily Hammond's flat where she has been found murdered. Ripley notes that Emily is divorced with no kids and that there were no signs of forced entry, suggesting that she may have knew her attacker. When Luther learns that she was returning from a speed dating event he is skeptical that she invited her attacker in. They examine the body which has been dressed in black leather and fishnets. The killer has also placed a wig and a crude mask on her. Ripley notes that there is no S&M paraphernalia in the flat to suggest that she was into that fetish. Luther says that dressing her up in such a way is very specific and meaningful to the killer. He notes that marks on Emily's feet indicate that she was wearing shoes when she was killed but that the shoes seem to be missing. Luther also notes that the outfit she is dressed in is reminiscent of the "post-punk" scene in the early 1980s. He mentions that he's seen something similar before but can't remember where. Ripley and Luther speculate that the killer may be reenacting an old murder.
Luther is taken aside by his supervisor DSU Martin Schenk. Schenk tells luther that he has been ordered to assign Luther to the murder of Jared Cass, an unemployed "cyber activist" who was murdered last night. Someone taped a video on Cass's cell phone forcing Cass to apologize. Luther tries to beg off saying that the killer of Emily Hammond will only continue killing, but Schenk tells him that he has his orders.
Ripley is called to a meeting with his former coworker DCI Erin Gray who now works for internal affairs. She takes him to meet DSU George Stark, a retired police officer who says he has been brought out of retirement for a "special case". He lays out a series of killings which he believes Luther is responsible for, including that of Toby Kent. Stark accuses Ripley of being an accomplice and threatens him with being charged as an accessory to Luther's crime. Stark angrily begins to choke Ripley and then tells him "It doesn't feel nice does it? Someone who is supposed to uphold the law operating out of their own sense of justice." Gray gives Ripley the file on Toby Kent's murder and asks him to read it.
Luther discovers that the murder of Emily Hammond is similar to the crimes of the "Shoreditch Creeper", an unidentified man who assaulted several women between 1978 and 1981. At first he tied his victims up and masturbated while sucking their toes, afterwards stealing their shoes. He later escalated to murder, killing three women before stopping in 1981. Luther notes that such a killer would not have stopped killing of his own accord. However, the suspect was described as in his mid thirties at the time of the crimes, which would make him in his 70s now. Luther doesn't think that sounds right for Emily Hammond's killer.
Luther gets in a minor traffic accident with a pretty blonde woman. He exchanges information with her and insists that it was all his fault but says he has to get to a crime scene and leaves.
Ripley notes that if Gray and Stark had any evidence they would have arrested Luther already. Gray says that if Luther is really innocent, Ripley should prove it by wearing a wire while Luther investigates the Jared Cass case.
Schenk informs Luther that the Shoreditch Creeper case had been investigated by a DCI Ronnie Holland who is now retired. Luther suggests that although Holland may not have made an arrest in the case he likely remembers who his prime suspects were. Schenk, who knew Holland, says that he will go and talk to him.
At the Cass crime scene, Luther notes that Cass was living past his means. He and Ripley track down Sean "Beamie" Beamish, a loan shark who Cass owed money to. Luther accuses Beamie of killing Cass while trying to extract payment from him. Beamie angrily attacks Ripley and tries to get away, but Luther catches him and holds him over the edge of a balcony, asking him questions about the case. Gray and Stark listen in on the wire as Luther implies that he might frame Beamie. However, he stops just short of saying outright that he will do so. Beamie admits to being as Cass's flat but says that Cass was already dead when he got there and he simply robbed the place to get back some of the money he owed him. Beamie gives them Cass's laptop and mobile phone. He tells them that Cass made plenty of enemies by trolling people online.
Mary Day, the woman who Luther had the traffic accident with calls him and tells him that the accident was her fault since she was tuning the radio at the time. He still insists that he take the blame and she offers to buy him a drink.
Ripley and Luther go to interview Ken Barnaby, a man who Cass had taunted online. Barnaby explains that his daughter had died of an epileptic seizure and that soon afterwards they had started receiving taunting messages online. Overcome by emotion, Barnaby goes in the other room and breaks down. Luther goes to comfort him. Barnaby's wife says he was in all night with her the night of the murder. Ripley thinks that Barnaby has motive and a weak alibi but Luther refuses to pursue it.
Schenk arrives at Ronnie Holland's house and finds him dead on the floor. Luther observes Ripley meeting with Gray. She warns Ripley that Luther might be suspicious. Gray notices Luther watching them surreptitiously and kisses Ripley to imply that his secretive behavior is due to their seeing each other. Gray tells Ripley to push the issue with Ken Barnanby in order to make Luther make act.
Schenk explains that Holland had been dead for months. The mask which Emily Hammond was wearing does not appear to match anyone in the files related to the Shoreditch Creeper. Schenk suggests that Emily reminds the killer of the woman who the mask is based on. Luther then realizes that they're looking at things the wrong way. Emily was always the intended victim. The mask was meant to make her look like she did back in 1982.
Emily's killer approaches the house of Dani and Craig Lane at night. Some time later, Craig searches for the couple's cat Smokey and Dani gets up and looks out the window, as if someone might be out there.
Schenk discovers information about Emily Hammond in files which Ronnie Holland kept about crimes which might be related to the Shoreditch Creeper. In 1982, when Emily was 14, she had lived in Shoreditch with her mother. One night, when she was sleeping, a man broke in. A lodger in the house returned home with several friends and chased the attacker off. The lodger's name was Dani Shahi.
Ripley calls Luther and says that he's found the SIM card from Jared Cass's phone in the garbage chute at his flat. The killer had removed the card after filming Cass's confession, something which would be impossible to do with gloves on. There's a clean print on the card. Luther calls Ken Barnaby, informing him that they do not have his prints on file and that he should come in the next day to give his prints. After hanging up, Barnaby goes into his kitchen, starts a blender and sticks his hand into the blades. Afterwards, Ripley tells Gray that Barnaby will lose his hands. Gray says that since he's lost his finger, they can't compare it to the print they found and Barnaby will likely be acquitted if he's brought to trial. Ripley confronts Luther, accusing him of warning Barnaby about the print. He punches Luther.
At the Lane house, Craig searches for their cat while someone secretly watches Dani undress for bed. In bed the couple begin to make out when they hear a strange mewling from the attic. Dani starts to call the police but Craig says it's just the cat. He goes into the attic to find him and is attacked by the man who killed Emily Hammond. The two men fight and the attacker eventually shoves Craig's head through the floor into the bedroom below. Dani, screams and starts to run out, but the hallway is blocked by the pull down stairs from the attic. Instead she hides in a closet. She watches as the attacker descends from the attic and appears to leave. Just then, the attacker rips open the door to the closet and Dani screams.
Luther calls Mary Day and asks to take her up on her offer of a drink.
Ripley returns to meet with Stark and tells him "You're right. Someone has to stop him."