The Velvet Target by Genevieve Holden, 1956 Paperback
First paperback edition from Ace Books.
Eve Halsey, sure that her Aunt Blossom's new husband, John Lanham, is a Bluebeard, alerts detective White to her suspicions, and then when she is alone with Lanham wakes up to the unhappy truth that it is she- rather than Aunt Blossom will be his victim. Lanham's nephew, also a calculated casualty, shares her status and together they are almost able to escape- while white works on the outside to move in at the finish. A more than tense situation- and a bright tone to the dialogue.
Book is very nice with minor tanning of pages from age.