In the novel N or M?, Mr Walters is a resident of Leahampton, and an acquaintance of Tommy and Commander Haydock.
Mr Walters and Dr Curtis pass Commander Haydock's house on the way back from a walk on the headlands. Tommy walks with them to the gate of Sans Souci, and they converse with him about various local matters.
After Tommy disappears, Mr Walters tells the police that Tommy had walked with him and Dr Curtis as far as the gate of Sans Souci, had said goodbye, and had turned into the drive. That was the last time Tommy had been seen before he disappeared.