In the novel N or M?, Farquhar was working in British intelligence during World War II. According to Mr Grant, he was the best man they had, or were likely to have.
He was hit by a lorry, and only lived a few hours after that. Unconscious he was taken to St. Bridget's Hospital, but it was too late to save him. Just before he died he uttered the cryptic words: “N. or M. Song Susie”.
According to Mr Grant, Farquhar's death was not an accident, which gave reason to believe that he was on to something. However, he had been methodically following up one line after another, most of which led nowhere, and they knew next to nothing of what he had discovered.