I've just been reading Leonard S. Marcus's wonderful Listening for Madeleine: A Portrait of Madeleine L'Engle in Many Voices (2012). I learned in the introduction that L'Engle's father, Charles Wadsworth Camp, was a mystery author of some renown! Did you know that? I sure didn't.
He wrote about a dozen mystery books under the name Wadsworth Camp, including Sinister Island (1915), The House of Fear (1916), The Abandoned Room (1917), and The Gray Mask (1920). Many of his works are now available digitally for free at http://manybooks.net/authors/campw.html.
Several films were made from Camp's stories and novels, including The Last Warning (1929), based on The House of Fear and starring Laura La Plante.
I don't generally think of Madeleine L'Engle as a mystery author, but The Arm of the Starfish (1965), Dragons in the Waters (1976), and Troubling a Star (1994) would all qualify as mysteries (and indeed, they all get the subject heading "mystery and detective stories" in WorldCat.)