Dr Lancelot Priestley is a fictional investigator in a series of books by John Rhode.

After 1924 Dr Priestley took over from Dr Thorndyke

Dr Thorndyke

Dr John Evelyn Thorndyke is a fictional detective in a long series of novels and short stories by R. Austin Freeman . Thorndyke was described by his author as a 'medical jurispractitioner': originally a medical doctor, he turned to the bar and became one of the first - in modern parlance - forensic...

 as the leading fictional forensic investigator in Britain, and featured in over 50 novels written over 40 years, solving many ingenious and misleading murders, usually at the request of the police but only if the case piques his scientific curiosity, having little interest in criminal justice. In the early books Dr Priestly provides assistance mainly to his friend Chief Inspector Hanslet. In later books Dr Priestley becomes an armchair detective

Armchair detective

Armchair detective is a term used for a fictional investigator who does not personally visit a crime scene or interview witnesses; instead, he or she either reads the story of the crime in a newspaper, or has it recounted to him by another person. As the armchair detective never sees any of the...

 and the bulk of the legwork is done by Superintendent Jimmy Waghorn of Scotland Yard

Scotland Yard

Scotland Yard is a metonym for the headquarters of the Metropolitan Police Service of London, UK. It derives from the location of the original Metropolitan Police headquarters at 4 Whitehall Place, which had a rear entrance on a street called Great Scotland Yard. The Scotland Yard entrance became...

and his secretary and companion, Harold Merefield. Harold Merefield is engaged to Dr Priestly's daughter April. Chief Inspector Hanslet (now retired) appears in several later works as a dinner guest of Dr Priestly passing on his professional wisdom to Waghorn.