Though this is book 3 in the series, I had to begin here, as I am perpetually subject to Egyptomania.
Olive Belgrave, a gentlewoman earning her living as a private detective in 1923, is an engaging protagonist. In this one, she is hired to investigate the suicide of Lord Malvern, an Egyptologist. The historical aspects seem to be quite well researched, so it is informative on the time period, as well as an entertaining mystery.