The Secret of the Minstrel's Guitar

The Dana girls, Jean and Louise, join their friend Isabel and her father on a trip to Lisbon, Portugal. Their vacation quickly turns into a double mystery when they are asked to help solve baffling thefts from a cork warehouse. Even before their ship leaves New York, the girls encounter a puzzling situation involving a minstrel's guitar and a determined thief, leading them to wonder if these events are connected to the warehouse crimes. Combining sightseeing with detective work, Jean and Louise must outwit sinister figures to solve both mysteries.