In the novel The Clocks, Angus McNaughton is Scottish and a retired Cambridge mathematics professor, occupant of 63 Wilbraham Crescent. As part of his property adjoins that of No. 19, he was questioned by the police as a potential witness when a dead body was found there.
McNaughton is an avid gardener. At the relevant time, he was working in his back garden. He heard a scream (that was Sheila Webb discovering the body and running out of No. 19). However he does not wear his watch while gardening and so did not know the exact time.
Later, the counter-espionage agent Colin Lamb asks his superior Colonel Beck to have several individuals vetted including the professor. The vetting process revealed that McNaughton was who he said he was. He had retired from his Cambridge position rather suddenly on grounds of ill health but appears completely healthy. After retirement, the professor appeared to have cut himself off from all his old friends, which Colonel Beck found rather odd.
Colin Lamb later surmised the real reason for his sudden retirement.