Open Road $1.99 at Kindle US, one was new to me. Not at Kobo US, at least so far.
Most Secret, apa
Devil Kinsmere, by John Dickson Carr (written as Roger Fairbairn):
https://www.amazon.com/Most-Secret-J...dp/B00ISH782U/
Wrack and Rune, Peter Shandy #3, by Charlotte MacLeod:
https://www.amazon.com/Wrack-Rune-Pe...dp/B009S33LRO/
The Girl in the Cellar, 32nd and last in the Miss Silver series by Patricia Wentworth:
https://www.amazon.com/Girl-Cellar-M...dp/B00AG8GU46/
Murder, Stage Left, by Robert Goldsborough, 12th and most recent in Goldsborough's continuation of Rex Stout's Archie Goodwin/Nero Wolfe series:
https://www.amazon.com/Murder-Stage-...dp/B01KJ2BXF4/