The Adventure of the Priory School

The powerful Duke of Holdernesse's son is missing. The boy was last seen in the Priory School but shortly after he received a letter from his father, he was nowhere to be seen. The main suspect was the German master because he went missing the same day as the boy. The Priory School's director reached out to Watson and Holmes who followed after the boy's steps. Will they solve the case and find the boy? Did the boy went somewhere by himself or someone kidnapped him? Find the answers in "The Adventure of the Priory School" which is a part of "The Return of Sherlock Holmes".