In the novel Destination Unknown, Mrs Olive Betterton is the second wife of the scientist Thomas Betterton. At the time of the events of the novel, she had been married to him for six months. She was a tall woman of approximately twenty-seven years of age, with auburn red hair, blue eyes, and a face which seemed "almost insignificant". She is first introduced when she asks Mr Jessop if there are any news of her husband. He tells them there aren't, but asks her several questions about her husband.
She last saw Thomas on the 23rd of August, when he left England to attend a conference in Paris. He did, but on the third day he told his colleagues he was going for a trip on a bauteau mouche, and then disappeared. Olive believed it was possible that he was kidnapped, or that he lost his memory.
After the interview with Jessop, she tries to join his husband but dies in a plane crash while trying to do so. Jessop then contacts a woman who wanted to end her life, Hilary Craven, to pose as Mrs Betterton. The real Mrs Betterton dies in the aviation incident under the name of Craven, and Hilary poses as her to continue her trip - this was described by Jessop as an "alternative to throwing yourself in front of a train or something like that". He gives her a series of details about Olive's life wich she had to learn by heart, such as the names of her dog and her canary.
Hilary later meets Olive Betterton in her deathbed and asks her if there is any message she'd like to give to her husband. Before passing away, she replies with:
"Tell him - tell him - to be careful. Boris - Boris - dangerous... Snow. Snow, snow, beautiful snow! You slip on a lump, and over you go! Go... Go? Go and tell him about Boris. I didn't believe it. I wouldn't believe it. But perhaps it's true... If so, if so..."
Her last words are not properly explained, but there is a partial answer in Chapter 7, when Henri Laurier asks Hilary about the weather and she replies with Olive's last words. This was probably a password, because after pronouncing those words she travelled to the research facility where her "husband" was staying. About "Boris", the words refer to a cousin of Thomas' first wife, Boris Glydr, but there are no other explanations.