It’s 1973 in Hackney, London. Detectives Len Bradfield (Sam Reid) and Spencer Gibbs (Blake Harrison) respond to an anonymous tip and find a teenage girl’s body in the underground parking garage of a housing complex. The victim has been strangled with her own bra. They notice track marks on her arm, and assert that she must be a drug addict. Finding the Jane Doe’s identity is their top priority.
We meet Jane Tennison (Stefanie Martini) as she rides the bus to work as a “WPC,” or woman police constable. She abruptly exits the bus to chase down a purse snatcher and help the victim, which causes her to be late. She is assigned menial duties at work, including fetching tea, directing traffic, and working as a dispatcher with her friend and fellow officer Kath Morgan.
Tennison joins the murder investigation when she is asked to help a house-to-house investigation of the area. When she knocks on one particular door, she unexpectedly encounters the woman whose purse was stolen that morning. The woman’s son comes to the door and acts strange when he sees the drawing of the victim, triggering Tennison’s suspicion.
After visiting local addiction hospitals, detectives identify the victim as 17-year-old Julie-Ann Collins. Tennison and Morgan confirm the victim’s identity with local prostitutes, who reveal that Julie-Ann used to work with them and was dating a man with “brown hair and a bad leg.”
Detectives find a group of addicts at Julie-Ann’s last known address and bring them into the station for questioning. None of their finger prints are found on Julie-Ann’s body. One of the men, Eddie Phillips, claims to have been Julie-Ann’s boyfriend. He says he dropped Julie-Ann off at the hospital to get clean two weeks earlier, and hasn’t seen her since.
Bradfield recruits Tennison to join him as the female presence on a next-of-kin visit. It’s Tennison’s first assignment and she’s nervous. Bradfield encourages her to follow her intuition and ask questions to become a better officer. As they make small-talk, Jane reveals that she’s a “posh sort” from a wealthy neighborhood.
Bradfield and Tennison break the news to Julie-Ann’s horrified parents. Her father formally identifies her body. He tells the detectives that Julie-Ann did not live at home and that he had not spoken to his daughter in over a year.
Meanwhile, career criminal Clifford Bentley (Alun Armstrong) is soon to be released from prison. He tries to negotiate with kingpin Clay Whiteley to change the details of an upcoming robbery that they have been planning from the inside. We learn that Bentley’s wife is the purse-snatching victim from that morning, and that Whiteley was responsible for the assault. Whiteley threatens to seriously harm her if Bentley tries to back out of the robbery.
At home, Jane’s mother is concerned about Jane’s work schedule, use of birth control, and lack of personal life. She wishes Jane were more like her younger sister Pam, who is soon to be married. But despite her mother’s protests, ambitious Jane is determined to make a difference in the world as a police officer.
The next day, brothers John and David Bentley gather information about a local bank. David looks mournfully at a newspaper article about Julie-Ann’s murder, and John encourages his brother to “forget about her.” David and John are the sons of Clifford Bentley, and are presumably involved in the imminent robbery.
A more sober Eddie Phillips is interrogated again by Bradfield and Gibbs. Phillips confirms that he dropped Julie-Ann off at the hospital, but that he saw her panic and leave with an unknown person in a red Jaguar. Eddie is adamant that he did not kill Julie-Ann, but Bradfield isn’t convinced. Nevertheless, the detectives start the search for a red Jaguar.
Bradfield brings Tennison to the morgue to assist with Julie-Ann’s autopsy. The coroner shows the detectives a green beaded bracelet that Julie-Ann was wearing when she died, and red carpet fiber found on the soles of her socks. They determine that Julie-Ann was brutally beaten days before her death, and that she was pregnant when she died.
Back at the station, Eddie Phillip’s grandmother berates the officers for implicating Eddie in the murder. She tells the officers that Eddie borrowed money on Julie-Ann’s behalf once, and that her inability to pay it back resulted in him being assaulted. She also provides an alibi for Eddie on the night of Julie-Ann’s murder, but it doesn’t match his original story. Bradfield is suspicious and tries to bring Eddie back in for questioning, but the suspect has disappeared.
Tennison returns to the street corner to further question the prostitutes Julie-Ann used to work with. A girl named Suzy tells Tennison that Eddie had Julie-Ann “trapped.”
Eddie Phillips appears at the Collins home to talk to Julie-Ann’s father.
Tennison finds Bradfield in a bar and the two share a drink. Bradfield reveals that he has a personal vendetta against Clifford Bentley, who once killed a fellow police officer. Tennison walks Bradfield home, and he kisses her. He immediately identifies the gesture as a mistake, as he’s her superior officer.
The next day, Tennison calls local garages to search for the red Jaguar that picked up Julie-Ann. WPC Morgan finds one owned by a Doctor Hussein Pryor, who works at a drug treatment program. The doctor confirms that his ex-wife owns a red Jaguar, but points the detectives to the nursing staff. One of the nurses, Mrs. O’Duncie, confirms that she let Julie-Ann use a hospital phone. The detectives go to the hospital and retrieve a pad that Julie-Ann used to write down a phone number, although the relevant page is missing. A partial number is later recovered with the help of forensics.
The Bentley brothers smuggle heavy construction equipment into a Greek restaurant located next to the bank. When the owner expresses hesitation, they imply that he will be getting some of the profits from a heist. The brothers wistfully dream about what they will do with their shares of the cash, both anxious for fresh starts. Under cover of night, they start digging through the restaurant’s wall, in the direction of the bank.
The search for Eddie Phillips continues as the detectives pursue a possible friend of his: Dwayne Clark. A covert drug squad identifies Dwayne Clark as Darren Ackroyd, a known drug dealer. The detectives find Clark and bring him in for questioning, but the dealer is smug and denies knowing Eddie Phillips. Clark’s car contains a substantial amount of illegal substances and a “tally book” of Clark’s transactions. The covert officers give the detectives surveillance photos of Julie-Ann with Eddie and his drug supplier, known on the street as “Oz.”
Bradfield and Tennison make an appearance at Julie-Ann’s funeral. When Tennison uses the Collins’ telephone, she realizes that their phone number matches the partial number taken from the hospital notepad. Emboldened, she sneaks into the Collins’ garage, and finds a red Jaguar. Bradfield gets a search warrant.
Now forced to tell the truth, Julie-Ann’s father, George, confirms that he and his daughter did talk the day she left the clinic. He maintains that their conversation was brief and that he did not pick his daughter up from the hospital. Suddenly, in the Collins home, Gibbs finds blood and scratch marks in a bedroom with red carpet. Bradfield chillingly asserts that Julie-Ann was locked in the room. The detectives arrest George Collins.