Freeman Wills Crofts 
The Box Office Murders 

A girl employed in the box office of a London cinema falls into the power of a mysterious trio of crooks. A helpful solicitor sends her to Scotland Yard. There she tells Inspector French the story of the Purple Sickle. Her body is found floating in Southampton Water the next day. French discovers that similar murders have taken place. After gathering evidence he learns the trio s secret and runs them to ground.