Diana Brinton

In the novel Towards Zero, Diana Brinton is a thirteen year old girl staying at the Easterhead Bay Hotel with her dog Don. There she is befriended by Angus MacWhirter, also staying at the hotel. He helps her with a particular problem. Diana's dog Don had rolled over some dead fish on the beach and this had given him a highly unpleasant smell which could not be removed even after being bathed with sea water. Angus suggested that only hot water and soap would work and helped Diana smuggle the dog into his hotel room which had a bath. This smell of dead fish stuck in Angus's memory and would later become an important clue for him in the solution of the crime.

Agatha Christie's Marple
In the 2007 ITV adaptation of the story. Diana is portrayed by Eleanor Turner-Moss. She is older than the Diana in the book but also has the same problem with her dog, named Donald in the show. As Angus MacWhirter is not featured in this adaptation, she is befriended by Miss Marple instead. The clue of the smell is developed differently. Here, instead of Angus getting the wrong suit back from the cleaners with the smell on it, Diana tells Miss Marple that she was looking for her dog who had wandered off and encountered the smell in the billiard room where Ted Latimer and Nevile Strange were playing billiards.