In the novel N or M?, Major Bletchley is one of the residents at Sans Souci. Tuppence finds him so stereotypical of an old ex-military officer, that she wonders if he really is genuine. Tommy found him easy to befriend, provided one is willing to listen to his incessant accounts of service on the Northwest Frontier and how he would conduct the present war better. Major Bletchley is a keen golfer and invited Tommy for a round of golf. During the game, Bletchley introduced Tommy to Commander Haydock who invited both of them to his house at Smugglers' Rest.
When Betty Sprot is kidnapped, Major Bletchley assumes control of the situation, and wants to call the police. When Mrs Sprot refuses to let him do so, the residents of Sans Souci form a party to go after Betty themselves. Major Bletchley is part of the party, and suggests getting Commander Haydock to help them, as he has a car.
Major Bletchley owns a pistol, and keeps it in his room in Sans Souci. This is the gun with which Mrs Sprot shoots Vanda Polonska.