I've read quite a few Heyer mysteries so far but I think I've just found my favorite -- Footsteps in the Dark. Sadly, it wasn't Heyer's favorite. I found this on Wikipedia --
The following year , Heyer's writing took an even more drastic departure from her early historical romances when she released her first thriller, Footsteps in the Dark. The novel's publication coincided with the birth of her only child, Richard George Rougier, whom she called her "most notable (indeed peerless) work". Later in her life, Heyer requested that her publishers refrain from reprinting Footsteps in the Dark, saying "This work, published simultaneously with my son ... was the first of my thrillers and was perpetrated while I was, as any Regency character would have said, increasing. One husband and two ribald brothers all had fingers in it, and I do not claim it as a Major Work."Well, at least she loved her son! This is a pretty standard Heyer mystery as far as plot goes--English country house, far-fetched mystery, bumbling country police officer and the inevitable romance--but the execution was more solid than usual. The characters were less stereotyped and had a bit more depth than in her later mysteries and the romance was more believable. So, even though Heyer didn't want it reprinted, I'm glad that Sourcebooks did it anyway.
A good story is no mystery,