From end of Casefile #13 -- When the Hardys win an all-expenses-paid trip to sunny Spain, they look forward to playing on the beach. But when their tour guide disappears and foreign agents start closing in on them, playing is more work than it seems. Frank and Joe investigate their "good luck" in winning the contest -- and in meeting Elena, a beautiful Spanish girl. The more they dig, the more it looks as if they've been set up in a dangerous game of espionage. Still worse, both sides now consider them security risks -- and in the spy business, security risks don't live to a ripe old age! Can Frank, Joe, and Elena clear themselves? Or will rival spymasters clear them off the board?

From back of book -- When Frank wins an all-expense-paid vacation to Spain's Costa del Sol, the brother detectives are set for some good times in the sunny paradise. But instead of flamenco music and bullfights, Frank and Joe find themselves running from the law. It seems their official tour guide has been murdered, and the evidence points directly at them. To make things worse, the Hardys are also being hunted as spies by the KGB -- and as traitors by the Network. Trapped in very tight spots, Frank and Joe need every ounce of daring and skill...to keep from being shipped home in matching boxes.