In the novel The Body in the Library, Ruby Keene (real name Rosy Legge) was a dancer at the Majestic Hotel in Danemouth. She was a cousin of Josie Turner. Before working in Danemouth she was a dancer at the Palais de Danse in Brixwell, South London.
She was eighteen years old, and was five feet and four inches tall. She was slender, and had platinum-blonde hair, blue eyes, and a retroussé nose.
When Josie injured her ankle, she was unable to dance her nightly exhibition dances with Raymond Starr, so she asked Ruby to take over the dancing. Ruby went down well, and got on especially well with the older men. She spent a lot of time with Conway Jefferson and his family, and he sometimes took her out for drives.
Conway became so fond of Ruby that he decided to adopt her legally. About ten days before the events of the novel, he made a new will leaving fifty thousand pounds to be held in trust for Ruby until she was twenty-five, when she would come into the principal.
Ruby was initially discovered to be missing when she did not turn up for her midnight exhibition dance with Raymond. She had earlier danced one exhibition dance with him, and had also been seen dancing with a young man named George Bartlett. Josie and Raymond searched for her, but she was not in her room. When she was still missing the next morning, and her room had not been slept in, Conway Jefferson got very worked up, and insisted that the police must be notified.
On the night of the murder, Ruby had been drugged. Miss Marple suggested after-dinner coffee as a probable vehicle for the drug. She had been told to change, and go to Josie's room and wait. When Josie went upstairs, she killed Ruby.
In BBC 1984 adaptation of the novel which formed part of the Miss Marple series, Ruby is played by Sally Jane Jackson. Most of the scenes with her are in flashback as she is already dead at the beginning of the show.
In the ITV 2004 adaptation of the novel (Episode 1, Season 1 of Agatha Christie's Marple), Ruby is played by Emma Williams.