The Problem of the Wire Cage, by John Dickson Carr

A very appealing and cleverly constructed 1939 whodunnit, with a bit of an un-fair trick to it, but still, very clever and fun. The body of obnoxious Frank Dorrance is discovered- after an afternoon filled with tennis and threats- dead in the center of the clay court, with only one set of footsteps leading to the body. Dr. Fell, Carr's hero, works out how it was done, with some very Nancy Drew-ish red herring characters along the way. Very enjoyable.