In the novel A Pocket Full of Rye, Jennifer Fortescue, usually known as “Mrs. Val” is the very bored wife of Mr. Percival Fortescue and a leading suspect in the murder case of Rex Fortescue. She is a former hospital nurse. Percival apparently fell in love with her after she pulled him through pneumonia, and he proposed marriage. Rex Fortescue, who was a snob, despised his daughter-in-law, as he felt that she was not a good match for his son. She thoroughly disliked him in return - which gives her a motive for murder, if an unlikely one, given that the younger Fortescues are due to move into a house of their own quite soon.
A much better motive presents itself when it is revealed that Jennifer is in fact the daughter (Ruby MacKenzie) of a former partner of Rex Fortescue, whom he left to die in the wilds of Africa.
Jennifer's chief interests are shopping and going to the cinema. Unfortunately her husband keeps her shorter of money than she'd like.
Jennifer is described as a "plump woman with a discontented mouth". She is about thirty years old. When she first hears of the death of Rex Fortescue from Inspector Neele, she eagerly asks him about it. Inspector Neele perceives that this is not a ghoulish satisfaction, but an indication that she is very bored. She has achieved leisure by marrying a well-to-do man, but it has not satisfied her.
It is later revealed that Jennifer is in fact the daughter (Ruby MacKenzie) of Mr MacKenzie, a former partner of Rex Fortescue, whom he left to die in the wilds of Africa. Her mother, Helen MacKenzie, believed that Rex was responsible for the death of her husband, and made her children swear every night that they would kill him. However, when Jennifer entered the nursing profession, she realised that her mother's mental balance was not what it should be.
When Percival had pneumonia, a friend of Jennifer's got the job of nursing him. Jennifer got her friend to leave, and to propose her as a replacement. This gave her the opportunity of seeking revenge for her father's death. When Percival became fond of her and proposed marriage, she decided that marrying him would be a far more sensible way of getting revenge. However, this greatly angered her mother, who felt that she had not kept faith.
It is further revealed that Jennifer was the one who had put blackbirds in the pie, and on Rex's desk, the summer before the events of the novel. Rex had been talking about how he had swindled people without doing anything illegal, and she had wanted to give him a fright.
Inspector Neele also discovers that Mary Dove had blackmailed Jennifer. Miss Dove had said that she would continue letting Inspector Neele think that she was Ruby MacKenzie if Jennifer gave her money. Jennifer had sold some of her jewellery to get the money. Inspector Neele is able to get it back for her.
In the BBC 1985 adaptation of the novel which formed part of the Miss Marple series, the part of Jennifer Fortescue is played by Rachel Bell. In this adaptation, Jennifer has a separate bequest of 40,000 pounds from Rex Fortescue's will. Although Percival said he was indifferent to this idea, Adele Fortescue speculated that this was the cause for the big arguments the occasionally witnessed between Percival and Jennifer. Jennifer told Inspector Neele that she had simply asked Rex for the money on the grounds that Percival was mean to her. At the end of the show, Miss Marple speculated that Rex may have known for some time, or even all along, that Jennifer was Ruby Mackenzie. Jennifer also told Miss Marple at the end of the show that she planned to leave Percival, now that she had her money. In this adaptation, it appears that Jennifer is not estranged from her mother. She visits her at the snatorium--she told Miss Marple that she had heard from the nurse that Miss Marple had been kind to her mother. There is also no suggestion that Jennifer was being blackmailed by Mary Dove in this adaptation.
In the ITV 2008 adaptation of the novel (Episode 1, Season 4 of Agatha Christie's Marple), the part of Jennifer Fortescue is played by Liz White. The portrayal here is very faithful to the original story.