Clint Faraday Mysteries Book 32: Blood and Gold Collector's Edition

An elderly woman is murdered in her home in front of a large safe. Clint is able to open the safe when he finds the combination in a recipe book It is filled with gold bars marked as coming from Mexico in 1939. She had lived on Isla Colón for 30 years and had millions of dollars worth of gold in her house? Where did it come from? Who knew about it after 75 years?