The Spanish Prisoner letter is the oldest confidence game and Mr. Gruber is one of its senior practitioners with a very active item. Ryker who had resigned from the FBI (after a wrong arrest leading to an unnecessary suicide) finds the past catching up with him in Spain where a man is crucified on a Maltese cross and some gold, hidden in the dungeon of a castle, leads to further reprisals. Mr. Gruber writes with more assurance than his plot justifies but it's reliable currency, particularly when recirculated in paperback.