Murder for Two — George Harmon Coxe

Trying to help a wronged inventor, a friend of Casey's ends up murdered

The last thing Flash Casey needs is an apprentice. Turned down by the army because of a bum knee, he agrees to teach a twice-weekly photography class for the American Women's Voluntary Services. One of his students, whose father just happens to have a lot of money invested in Casey's paper, asks to tag along on an assignment. Flash can't say no.

An engineer named John Perry has come to beg for help from one of Casey's friends at the paper, crusading news columnist Rosalind Taylor. A few years back, Perry invented an industrial lubricant that should have made him a fortune, but his partner stole his idea and kept the profits for himself. Taylor has agreed to mediate for them, and asks Casey along to document the meeting. When Flash arrives, the apartment is ransacked and Taylor is dead. Casey will find her killers, as long as his little apprentice doesn't get in the way.