The following version of this book was used to create this study guide: Cleeves, Ann. The Darkest Evening. Macmillan, 2020. Kindle Edition.

Cleeve's narrative is divided into forty-six chapters, each told, with the exception of the first chapter, from the third-person perspective of either Detective Inspector Vera Stanhope, Detective Sergeant Joe Ashworth, Detective Constable Holly Jackman, or Vera's relative, Juliet Stanhope. The first chapter is told from the third-person perspective of Lorna Falstone.

On a snowy evening close to the winter solstice, Lorna Falstone dresses her son, Thomas, to go out. She thinks about the Christmas tasks she needs to do and of reconciling with her parents. However, there is matter that she has to resolve first. Lorna and Thomas leave the house. Later that evening, a man named Neil Heslop reports finding Lorna’s corpse on the Brockburn estate.

On the same evening, Vera realizes that she is lost as she drives home during the snow storm. Her choice of routes causes her come across a car on the side of the road. Thinking that the driver had an accident, she goes to help. However, the only person in the car is a toddler. She takes him with her with the intent of finding his mother and walks toward the lights given off by the Brockburn estate. Vera recognizes it as her ancestral home. Her deceased father, Hector, grew up there, but later became an outcast due to his behavior. Vera rings the bell and a woman named Juliet opens the door. Juliet is the daughter of Crispin, Hector’s brother’s son. Crispin is deceased as is his father. Juliet lives in the house with her mother Harriet and her husband Mark.

Juliet recognizes Vera because she attended Hector’s funeral. Vera’s appearance confuses her. They are having a dinner party to raise funds for a project that Mark has launched to save the estate, and Juliet wonders if Harriet invited Vera. Vera explains that she found the boy in the car and would like to use the phone to try to find his mother. Juliet takes her to the kitchen where a woman named Dorothy is cooking and two sisters, Nettie and Cath Heslop, are serving food. Dorothy tells them that their father, Neil, will be picking them up. When Neil arrives, he demands to use the phone to call the police. By now Holly, a member or Vera’s team, has already told Vera that the car belongs to Constance Browne. Constance has told Vera that a woman named Lorna Falstone sometimes borrows it and has confirmed that her car is missing. Vera is on the phone with Constance when Neil enters. Vera tells him that she is the police and they go to look at the body. The victim is Lorna Falstone.

Vera calls in her team and the investigation begins. Lorna’s son, Thomas, goes to live with Lorna’s parents, Jill and Robert. Vera’s core team consists of Joe, Holly and Charlie. She also works closely with the crime-scene manager and the pathologist. Interviews at the house reveal that a guest named Sophie and her husband knew Lorna. Lorna suffered from anorexia and was in the same private hospital as her husband’s brother. Sophie, who shares her job with Mark, ran drama workshops there. However, it turns out that the couple has nothing to do with Lorna’s death. Lorna was not associated with any of the other guests. Vera also learns that Lorna was killed at the crime scene after being knocked out or stunned somewhere else.

The investigation begins to focus on finding the identity of Lorna’s son’s father. No one knows who he is. Mark emerges as a suspect because he works part-time in Newcastle and rumor has it that Lorna’s lover was a fancy man in Newcastle. Neil’s son Josh emerges as a suspect because he liked Lorna, but she did not return his affections.

Juliet and Harriet become suspects when Vera discovers that Crispin had an affair with Jill. Rumor has it that he is Lorna’s father. The discovery that Crispin paid for Lorna’s hospital bills during her recovery and the appearance of a letter that Crispin left Harriet give credence to the rumor. Vera wonders whether someone killed Lorna because Lorna wanted her share of the inheritance and she was ready to go public with her heritage. DNA evidence later proves that Lorna was not Cripsin’s daughter.

Dorothy’s partner, Karan, is also a suspect. He is good-looking and engaging. He and Dorothy live in a cottage on the Brockburn estate, and he was alone with their young son on the night of the party. Dorothy and Neil’s wife, Rosemary, are also suspects. Dorothy may have killed Lorna out of jealousy if Karan was Lorna's lover. Rosemary may have killed her to protect Josh if she thought the two of them were getting too close.

During the investigation, a search of Lorna’s apartment reveals paintings of a mysterious cottage that is later identified as Jinny’s Mill. It is also on the Brockburn estate, and Mark proposed to Juliet there. Lorna called one of the paintings The Darkest Evening. The team does not find Lorna’s laptop and cell phone. Then someone murders Constance Browne. She seems to have left her home voluntarily. Vera believes that she knew the identity of the killer.

The murderer reveals his identity when he kidnaps Thomas and takes him to Jinny’s Mill. Vera knows that she will find him there and lets Joe and Holly know her whereabouts. Vera finds Thomas in Jinny’s Mill and lets the kidnapper chase her into the woods. He catches her and confesses. He is Neil Heslop and is trying to strangle Vera when Holly finds them and saves Vera’s life.

At the end of the narrative, Juliet tells Vera that she should keep in contact, and Vera says she will. Jill says that she can be Thomas’s honorary aunt. Vera tells Joe how she solved the mystery and decides that it is not yet time to retire.