Found this info in a Goodread review of The Circular Staircase.......
"Although her name may not resonate with the public today as much as it did a century ago, Mary Roberts Rinehart has most certainly left her mark on modern-day fiction. The originator of the so-called "Had I But Known" school of detective writing, Rinehart was, for many years, the most highly paid and popular female novelist in America. Her second novel (but first to be published), "The Circular Staircase," which was released in 1908, when Mary was 32, featured a relatively new kind of crime solver, a no-nonsense spinster in long skirts and with an abiding curiosity; though certainly not the first lady detective, the character, Rachel Innes, certainly helped pave the way for many others (the website Wikipedia currently has a list of almost 400 fictional female sleuths!). "The Circular Staircase" has been turned into a film on three occasions, and in 1920 was transformed into a play, written by Rinehart and Avery Hopwood, called "The Bat"; Batman creator Bob Kane has admitted that the Bat character was an inspiration for him. Want more? Roberts' 1930 novel "The Door" is thought to be the source for "the butler doing it." (Perhaps I should add here that the classic 1946 film "The Spiral Staircase" is in no way related to Rinehart's book, but was rather based on Ethel Lina White's 1933 novel "Some Must Watch.") Despite these influences and past fame, however, Rinehart was an unknown quantity to this reader, until I happened to read a very laudatory article on "The Circular Staircase" in the overview volume "Crime & Mystery: The 100 Best Books," in which author H.R.F. Keating sings its praises. Fortunately, Rinehart's classic (in addition to the author's first novel, 1906's "The Man In Lower Ten") is in print today to entertain still another generation of readers.