The Yellow Violet — Frances Crane

This third outing In the Pat and Jean Abbott series is set in the early weeks of World War II at a time when everyone smoked and women wore girdles. Private detective Pat is back home in San Fancisco hours away from marrying Jean Holly when a fellow detective is murdered in his office, the only clue a yellow violet. As it so happens, a beautiful Spanish entertainer, a refugee from the Spanish Civil War--whose trade mark is the yellow violet--is in town on tour accompanied by her mother, her manager, and a dachshund named Pancho. Throw in a few Italian fascists ("They don't fight very well," says Pat, "but they know how to spy") and you've got enough trouble to halt anyone's nuptials. First published in 1942.