L is for lawless (Pan Macmillan)

It was the week before Thanksgiving when Kinsey Millhone first heard the sad story of the late Johnny Lee, the World War II fighter pilot of whom, rather mysteriously, the military authorities have no record. His family are concerned -- perhaps Kinsey could make a few calls, straighten things out? Then Johnny's apartment is ransacked. In the debris a hidden safe is uncovered -- and in that safe is a mysterious key marked LAWLESS. That night Kinsey's on a plane to Dallas, at the start of a thrilling rollercoaster ride through Texas and Kentucky on the trail of long-buried treasure. Unfortunately there's a fire-raising psychopath on her tail...And she's going to be late for a very important wedding...'An alphabet of prime puzzles' Sunday Times