The Glass Mask (1944) by Lenore Glen Offord, Dell #198 mapback edition, 1947.
A Todd McKinnon book.
Lenore Glen Offord was a mystery writer and mystery reviewer in the San Francisco Bay Area. She won an Edgar Award for Outstanding Criticism in 1952. She published 12 novels, 8 of which were mysteries.
Read Gary Lovisi's article on Map Back Mysteries, here.