Rupert St. Vincent

In the short story The Listerdale Mystery, Rupert St. Vincent is the son of Mrs St. Vincent and brother of Barbara. After his father died, after losing all his money on speculation and leaving large debts, the family had been forced to sell their family home and move to a cheap boarding house in London. Then Mrs St. Vincent had sold their possessions to set Rupert up in a city job. The exact job is not described but according to the text, it is "on the bottom rung of office life", suggesting a job as a clerk in a city firm.

When Rupert's mother managed to rent a comfortable town house at a nominal rent, Rupert was suspicious. For one thing, the house belonged to Lord Listerdale, who disappeared under mysterious circumstances while staying at that house. For another, the nominal rent included the services of the servants and a butler and provisions seemed to appear for free for the family to use.

Rupert had a theory that someone had done away with Lord Listerdale and spent some time knocking at the panelling in the house looking for secret compartments where the body might be hidden. Later, he took a motor-cycling holiday with a friend named Anderson. Not having anywhere definite to go, Rupert suggested going to King's Cheviot, the country estate of Lord Listerdale in the hope that this might contribute to the solution of the Listerdale mystery.