NY: HarperCollins, 1964, 1936.
When I went through library school — back when that meant deep knowledge about books, not online databases — one of the requirements was several semesters of exposure to various genres of popular fiction, since you can’t recommend to patrons what you aren’t familiar with yourself. Mostly, when it came to mystery novels and detective stories, that meant the classic authors as they were in the 1960s: Ngaio Marsh, Ross MacDonald, Margery Allingham, John Dickson Carr, Dorothy Sayers, and especially Agatha Christie. I didn’t read mysteries as a kid (science fiction was my thing) but I discovered several authors whose work I could appreciate, and I’ve found many more since. But I never could handle Agatha Christie.