Sam Silver Undercover Pirate books

When Sam's crewmate, Harry Hopp, wins an ancient treasure map while playing cards, he is disappointed to find that the treasure lies at the heart of a famous cave complex. The treasure is legendary - and so is the fact that all those who seek it get lost in the labyrinth! Sam is convinced that with the aid of the map, he can find the treasure, but if he's wrong he could be doomed to wander the caves for ever...