After 1924, Dr. Priestley took over from Dr. Thorndyke as the leading fictional forensic investigator in Britain and featured in 72 novels written over 40 years, solving many ingenious and misleading murders.
Described in "The Ellerby Case", Dr. Priestley's book "Fact and Fallacy": ..contained in every one of its two hundred odd pages a direct and trenchant attack upon those whom the author was apt to allude to as "The Orthodox Scientific School".
Only in this way, as he more than once remarked, was it possible to maintain an impartial judgment"[4] In the early books, Dr. Priestley assists mainly his friend Chief Inspector Hanslet.
Superintendent Hanslet (now retired) appears in several later works as a dinner guest of Dr. Priestley, passing on his professional wisdom to Waghorn.
Lastly, an old friend of Priestley's, Dr. Oldland, in later novels frequently joins the conclave at the professor's Saturday evening dinners and provides the medical viewpoint attendant on the various cases.