Holmes and Vernier have been hired by the Baron of Creuse to find the legendary lost treasure of the kings of France.  Traveling throughout France along with a new companion, they must solve several intricate puzzles to unravel the mystery of the hollow needle.  They realize the answer lies to the north in Normandy, near the town of Étretat, but further complications arise, and Holmes must work with the notorious gentleman-burglar Arsène Lupin if he is to find the treasure and avoid a major international catastrophe.