The Spanish Cape Mystery (1935)

A rich family and a houseful of squabbling guests occupy a ritzy oceanfront mansion down on Spanish Cape. Beautiful Helen Twelvetrees and her eccentric uncle step outside to talk, only to be kidnapped and driven to a strange house down the road. The kidnapper knocks the uncle unconscious, then ties Twelvetrees to a chair, leaving her alone in the dark house while he hauls off the uncle somewhere in a boat.

Meanwhile, renowned mystery writer Ellery Queen is on vacation, accompanied by the retired judge who shares his interest in crime solving. They plan to get away from sleuthing but you know how it is for these amateur detectives....When they arrive at their vacation house, the first thing they discover is Helen Twelvetrees tied up in the bedroom. Like it or not, they're soon on the case.

Donald Cook is a flashy and debonair Ellery Queen. Berton Churchill is part assistant, part comic relief as his friend the judge. Helen Twelvetrees is fine as the young woman whose charming personality and family mystery both capture Ellery's attention. "Mr. Queen," she tells him at one point, "you have the oddest way of mixing romance and murder."

There is a murder and any number of suspects down at the mansion. A bumbling local sheriff sets out to untangle things ("Sit down a minute, Mr. Queen. I'll show you how a real detective solves a case") but soon enough welcomes Ellery's help. It all builds rather nicely to a climactic gather-the-suspects scene in which Ellery presents his deductions.

Overall it's very good, with just enough humor and a rather complex plot that actually makes sense.