Here’s an outline of what happens in the third book of the series, Career of Evil.

Spoiler warning: This page doesn’t name the killer, but it includes lots of details about the case and gives a full summary of Strike and Robin’s relationship throughout this book.

Career of Evil opens with a chapter from the point of view of an unknown person who has enjoyed murdering someone the day before. He observes Robin and her fiancé, Matthew, as they leave their flat and follows them when they catch a bus, all the time thinking about a plan he has to seek revenge on Cormoran Strike. 

The following Monday, Robin is on her way to work, dwelling on an argument she and Matthew had over the weekend. Sarah Shadlock, Matthew’s old university friend, had repeatedly brought up the subject of Robin’s working relationship with Strike in Matthew’s presence. Matthew is suspicious and resentful of Strike, and Robin tries but fails to make him understand that Sarah is deliberately causing trouble between them.

As she arrives at work, someone who appears to be a motorcycle courier hands her a large parcel. When Robin opens it in the office, she finds it contains the severed leg of a woman. Strike hears Robin scream and comes running down from his flat upstairs. He calls DI Wardle, who arrives shortly with DS Vanessa Ekwensi and a forensics team. While Wardle interviews Robin, DS Ekwensi finds a note hidden underneath the leg, containing a quotation from Mistress of the Salmon Salt by Blue Öyster Cult.

Strike tells Wardle that while he was in the military police, he gave anonymous evidence against a London gangster called Digger Malley, who has a reputation for posting body parts to his enemies. Wardle thinks it’s likely to be Malley who sent the leg.

Strike, however, has three other suspects he thinks are more likely to be responsible, all of whom have reason to harbour a grudge against him. Donald Laing, whom Strike investigated when he was in the army and sent to prison for a long sentence; Noel Brockbank, whom Strike also investigated when he was in the military police; and Jeff Whittaker, Leda Strike’s much younger second husband, who was tried but acquitted of her murder. Although they don’t usually speak about his parents, Strike confides to Robin that his mother had the same Blue Öyster Cult lyric tattooed on her body.

Press attention resulting from a police leak about the leg is having a detrimental effect on their business, so Strike and Robin decide to investigate these three suspects. Strike calls his old friend Shanker, a man with criminal connections, and asks him to look for Whittaker.  

As the package containing the leg was addressed to Robin, Strike and Robin agree she should be very careful and not work after dark. During a meeting in a pub, Strike notices a tall figure watching them from across the street. Another chapter from the point of view of the unknown killer reveals that he was the one watching them, and he is planning to murder Robin as an act of revenge on Strike. 

Strike meets Wardle for an update on the case. He hands Wardle two ‘nutter’ letters the agency has recently received, one of which is from Kelsey Platt — a girl who wants her own leg amputated. Wardle isn’t taking Strike’s three preferred suspects seriously and is still convinced the leg was sent by the gangster Malley.

Robin goes back to her hometown in Yorkshire for a wedding dress fitting. She and Matthew are still fighting and her mother, Linda, is concerned. She asks whether Matthew is jealous of Strike, and Robin confirms he is, but that she and Strike are just colleagues and friends. Linda then tells Robin that she’s getting a new car and offers Robin the old family Land Rover, which she accepts.

Strike asks a friend from the military police, Graham Hardacre, for information on the current whereabouts of Noel Brockbank and Donald Laing. Hardacre is stationed in Edinburgh and asks Strike to visit him there so he can pass on the information without too obviously breaking the rules.  In Edinburgh, Strike finds out that Brockbank gave his home address as Barrow-in-Furness when he joined the army, and since leaving the service had his military pension sent for a time to Manchester and then Market Harborough. Laing’s mother’s home address is in Melrose.

As Melrose isn’t far from Edinburgh, Strike takes the opportunity to visit and see if Laing is there. On the journey, he reviews his past encounters with Laing — including the investigation which resulted in Laing being sent to prison for severely abusing his wife, Rhona. Strike meets Rhona’s mother, who doesn’t know Laing’s current location but is eager to help. She fills Strike in on Laing’s family background.

Back in London, Robin arrives at the office, upset after a cataclysmic row with Matthew. She is telling herself she mustn’t cry because her work is all she has now, when Shanker arrives and startles her.  At first Robin thinks he’s the man who sent the leg, but Strike later assures her that Shanker would never hurt her. Whilst Shanker is telling Strike that his contacts believe Whittaker to be living in Catford, Robin leaves to conduct surveillance for another client.

Still distraught, Robin avoids all attempts by Matthew to contact her. Strike, who has noticed how upset she is, is also trying to reach her, but she does not respond to his messages and stays out working after dark against instructions. Not wanting to return home, she goes to The Tottenham, where she is found by the worried Strike.

Robin, having had a couple of glasses of wine, confesses to Strike that she has left Matthew. During their argument she found out that Matthew had cheated on her, sleeping with his friend Sarah Shadlock whilst they were at university. The timing of this affair is especially upsetting to Robin, as it took place after she had dropped out and was living back home with her parents. The wine and her emotional state, added to the realisation that Strike is her only friend in London and she needs his help, lead Robin to confide in Strike in a way she had not intended: She tells him that she was attacked, raped and left for dead at her student halls of residence. She’d had to leave university and spent a long time in her bedroom at her parents’ house before she began to recover and could face the world again. 

Robin is worried that Strike will now see her past trauma as a weakness, but inwardly he is astounded and impressed that she has managed to work on without interruption since the severed leg arrived.

Robin intends to find a budget room, but Strike is still worried she is a target of whoever sent the leg, so he insists she stay in a nearby hotel that he knows is more secure. Leaving the hotel, he chases a man he believes was following them but loses him. 

The following day, Strike and Robin are asked to come to Scotland Yard. The police have found the rest of the body in a flat in Shepherd’s Bush. The address is the same as that on letters written to Strike by Kelsey Platt although the flat is let in a different name. Fake replies from Strike were found in the flat. Strike and Robin don’t recognise the body when they’re shown photographs.

After the police interview, Robin offers to drive Strike in the Land Rover to Barrow-in-Furness to investigate Brockbank.  

On the journey, Strike tells Robin about Brockbank’s history. Brockbank’s stepdaughter, Brittany, told a school friend that Brockbank was having sex with her and had threatened to cut her leg off if she told anyone. In subsequent interviews with a female officer, Brittany denied the allegation, said her friend was mistaken or lying and refused to be physically examined. Believing Brockbank to be guilty, Strike punched him during the arrest and knocked him out. Later, he had a seizure and was eventually judged to be unfit to stand trial. There wasn’t sufficient evidence to charge Brockbank, and he left the army with his family, including Brittany.  

Holly Brockbank, Noel’s twin sister, is living at his old address. Robin goes undercover as a personal injury lawyer named Venetia Hall to interview Holly, who gives them some more background about Noel. He has been thrown out of more than one job for sexually abusing young girls. He pays his army pension to Holly in return for her silence.

Strike and Robin stay overnight at a Travelodge, five rooms apart. The next day they stop at Market Harborough, the last place that Brockbank worked, as a bouncer for a brothel. Strike pays one of the girls working there for Brockbank’s mobile number.

Wardle calls to let them know that the dismembered body has now been identified as that of Kelsey Platt, the girl who had written to them about her wish to remove her own leg. The tenant of the flat is abroad and appears to have no connection to the case. 

Robin and Strike travel on to Corby to see a woman named Lorraine who used to live with Donald Laing. Lorraine tells them he suffered from psoriatic arthritis and when he left her, he stole her jewelery. Strike suspects, from what Lorraine tells them, that he also beat up her elderly neighbour and robbed her house.

Back in the office on Monday, Robin tells Strike she has been pursuing an online investigation into members of the BIID (body integrity identity disorder) community in an attempt to find out more about Kelsey. She has also managed to get a lead on Laing — a Just Giving page in his name on which he claims to be raising funds for Arthritis Research. From a photo on the page, Strike and Robin deduce that Laing may be living in a flat in Elephant & Castle.

Robin calls Brockbank’s mobile number in her Venetia Hall persona. A young child answers and then a woman, who says that she will ask Noel to call Venetia back. Brockbank calls a few days later and initially agrees to meet in Shoreditch, but then apparently becomes suspicious and hangs up. Robin tells Strike she is concerned about Brockbank living in close proximity to a young girl.

Matthew, meanwhile, has stopped texting Robin begging for forgiveness and has returned to their flat acting in a calm and polite manner. Robin is unsuccessfully trying to find somewhere else to live.

Shanker comes to the office to tell Strike that his contacts have found an address for Whittaker in Catford, where he is living with a young woman who he has working as a prostitute. As Strike and Shanker talk, Robin opens a card addressed to her to find Kelsey’s severed toe taped inside.

Strike visits Kelsey’s sister, Hazel, at home at her request. She lives with her partner Ray, an ex-fireman. She gives Strike some background on Kelsey’s life.

Robin has been given the task of making a list of East End strip clubs and brothels in an attempt to track down Brockbank. She’s not pleased that Strike isn’t letting her go on surveillance — she’s convinced he thinks she’s not strong enough for the job now that he knows about her past attack.  Whilst working at home, Robin reconciles with Matthew.

Another chapter from the point of view of the killer shows him picking up, stabbing and mutilating a woman working as a prostitute.

Robin, against Strike’s instructions, returns to the office and gives him an ultimatum: She wants to work surveillance, not sit at home. They argue, and Strike relents. Strike is blindsided by her reconciliation with Matthew and thinks to himself that she’s making a huge mistake.

Wardle calls to say that they think whoever killed Kelsey has struck again and tells them about the attack on the prostitute, who has survived.

Over the course of the next week, Strike and Robin conduct unsuccessful surveillance on Laing’s and Whittaker’s flats, until Strike decides to follow Stephanie, Whittaker’s girlfriend. He encounters Whittaker and some companions who have been smoking crack in the back of a van, and they argue. Strike tries to persuade Stephanie to leave Whittaker and come with him; she refuses. Strike punches Whittaker.

Robin has managed to track down two members of the BIID online community that Kelsey belonged to. Strike and Robin interview them over lunch. They are Tempest, the creator of the online community, who uses a wheelchair although she is not disabled, and Jason, a young man who, like Kelsey, wants his leg amputated. They confirm they met Kelsey in London before her death and that she was picked up by her ‘boyfriend’ on a motorbike.

They are under the impression that Strike suffered from BIID and succeeded in getting his leg amputated, an impression that Strike angrily refutes.

Wardle informs them that the police have spoken to Laing’s neighbours who confirm he is suffering badly from arthritis and has been staying in Scotland. In consequence, they rule him out as a suspect.

Robin finds out at which strip club Brockbank has been working, but when Strike visits, he has already been sacked. However, he speaks to one of the women working there and finds out some information about Brockbank’s current girlfriend. Robin sees Laing at Elephant & Castle, walking with crutches.

Another chapter from the killer’s point of view shows him attacking, murdering and mutilating another victim. 

Wardle meets Strike and gives him details of the latest murder, plus information about previous murders they believe to have been committed by the same man. The police are now looking for a serial killer and although they cannot find any connection between the victims and any of Strike’s three suspects, Wardle now seems to be taking Strike’s suspicions more seriously and warns him to leave the suspects to the police. They are closing in on Brockbank, after an officer on a different case spotted him at a church in Brixton. They have also spoken to Laing, who has an alibi for some of the murders.

Robin is on surveillance outside Whittaker’s flat in Catford when she bumps into Stephanie, who has been beaten up by Whittaker. Robin gains her trust and manages to find out that Whittaker has an alibi for at least one of the killings. On her way back to the train station, she takes a wrong turn and is ambushed. Using her self-defence skills, she fights off her attacker but not before he inflicts a serious knife wound to her lower arm.

She is taken to hospital where Strike meets her. DI Roy Carver, who has replaced Wardle on the case, arrives and is furious that Strike is still investigating the case when he has been warned off by the police. As he leaves the hospital, Strike has a revelation about the identity of the killer.  

Strike later calls Robin, who is recuperating at home. He tells her that they must now abandon their investigation as a serial killer is a police matter. Robin urges Strike to go to Brockbank’s girlfriend, Alyssa, and warn her that she is living with a child molester. He refuses, as this would constitute interference as far as the police are concerned.

Robin can’t accept this and enlists Shanker’s help. She visits Alyssa and her two daughters at home, without telling Strike, and tries to tell her about Brockbank. At first Alyssa doesn’t believe what Robin is saying, but her eldest daughter tells her that Brockbank has ‘done it to her’. Brockbank arrives home and threatens Robin before Shanker chases him off with a knife and he disappears.

Carver telephones Strike, furious about what Robin has done and assuming that Strike put her up to it. The police believe they have found a link between the church in Brixton attended by Brockbank and Kelsey’s church, but they cannot question him since Robin has frightened him off. Strike tries to tell him his suspicions as to the identity of the killer, but Carver won’t listen.

Strike visits Robin at home and fires her from her job, citing gross misconduct. Robin is devastated.

Strike wants the killer brought to justice before he can kill again, but the police won’t listen to Strike. He sets up a plan to catch the killer himself, laying an ambush with the help of Shanker and Alyssa, who poses as his new secretary.

The plan is successful; Strike corners the killer, overpowers him in a fight and uncovers plenty of evidence to have him convicted.

He then asks Shanker to drive him to Masham where Robin and Matthew are marrying that day. He arrives late for the ceremony, battered and bruised, and as he enters the church, Robin is saying her vows. He accidentally knocks over a vase of flowers at the back of the church. Robin turns and sees him, smiles, and says ‘I do’.