Phantom Thieves: The Mystery of the Museum Robberies — Robert J. Trout

The idea of remaining in England and going on a tour of museums throughout England and Scotland, with the treasure of Robin Hood and the golden arrow he had won in an archery contest, strangely appealed to Ellen Allandale. Of course, she and her brother Carter also would be at the center of everyone's attention. Had they not solved the mystery of the hidden treasure and saved it from falling into the hands of the greedy descendant of the Sheriff of Nottingham, Baron Murdach? Even though the idea of greeting and speaking to large numbers of people made her nervous, Ellen quickly agreed to go. Little did she know that another mystery awaited her - a series of robberies at the museums that made her, Carter, and their Uncle Ruford the prime suspects. The only way to prove their innocence was to find the real thieves, a task that seemed impossible because both the thieves and their loot always vanished into thin air.