In the novel The Pale Horse, Bella Webb is the middle-aged cook of Thyrza Grey and Sybil Stamfordis who live in the village of Much Deeping in Devon. Bella lives with the two other middle-aged women in the house called "The Pale Horse", which was formerly an inn of the same name. Bella and the two others in the house are considered to be the "resident witches" in Much Deeping. Originally she is from the village of Little Dunning, and is twice widowed.
Like her employers, Bella also has a reputation of being a "witch" and dabbles in the occult. According to Thyza Grey, Bella works as a team with them, with each of them having different powers. Bella represents the "old English" aspects of witchcraft. During their rituals and seances, Bella would perform activities such as sacrificing a white cock while chanting spells.
When Mark Easterbrook and Inspector Lejeune finally exposed the role of the three women in the murder-for-a-price racket with their occult activities as a smokescreen, they conclude that Bella did not really understand her part in it and merely did as directed by Thyrza Grey. According to Mark Easterbrook, "Bella's belief in witchcraft is genuine ... She believes in her own powers and rejoices in them." In Thyrza's scheme, what Bella did was useful for creating "atmosphere". Certainly when Mark Easterbrook first met Bella, he found something in her stare that startled him. "There was malice in it, and a curious intimate knowledge." He noted: "I felt that without effort, and almost without curiousity, she had known exactly what thoughts were in my mind". Ariadne Oliver who was there with him also found Bella "disconcerting".
In the 2010 ITV adaption The Pale Horse (Episode 1, series 5 of Agatha Christie's Marple), Thyrza Grey and Sybil Stamfordis actually own and run an inn named "The Pale Horse". Bella is a works as a cleaner at the inn. Like in the original story, she also has a reputation as the "local witch" and performs acts such as sacrificing white cocks. Bella is portrayed by Jenny Galloway.