In the novel One, Two, Buckle My Shoe, Reginald Barnes is a retired civil servant. Like Hercule Poirot he is a patient at the dental practice on 58 Queen Charlotte Street. He shows interest in the case of the murdered dentist and the missing woman.
Mr Barnes is described as being a "small man with twinkling eyes and a nearly bald head". He speaks in a "small, prim, almost falsetto voice". He wears pince-nez. At the time of the events of the novel, he had been retired from the Home Office for some time. He lives at 88 Castlegardens Road, Ealing.
When Poirot calls on him, Mr Barnes expresses the opinion that what happened at 58 Queen Charlotte Street was an attempt on Alistair Blunt's life, by some organisation. He puts forward the theory that Mr Morley refused to assist the organisation, but had to be killed because he knew too much. He suggests that Mr Morley was probably asked to turn his patient over to his partner, Mr Reilly, but he refused.
Mr Barnes later calls on Poirot, who offers him coffee. Mr Barnes expresses the opinion that most English servants do not prepare coffee well, but he is sure that George will.
Mr Barnes tells Poirot about Albert Chapman, who was in Secret Service, and was useful because he was "an insignificant kind of chap", whose face was not easily remembered.
After Frank Carter is arrested, Mr Barnes tells Poirot that he did not expect the Mr Morley's death to be a private murder, as he was sure that it was something to do with Espionage or Counter-Espionage. He attributes this to being "mixed up in that sort of thing so much".
At the end of the novel, after Poirot has revealed the identity of the murderer, Mr Barnes reveals that Albert Chapman is a name he uses in his work as an intelligence agent. He had been interested in knowing about the aspects of the case involving Mrs Albert Chapman because he knew that he had never had a wife.