In the thrilling and exciting conclusion to the Improbable Tales of Baskerville Hall trilogy, a standout kids detective story, Arthur travels to the Lakes, a place more mysterious than the enchanting Baskerville Hall itself, and must do the unthinkable: betray his friends and Sherlock Holmes or pay the ultimate price. Perfect for fans of the Winterborne Home for Vengeance and Valor series and the Mysterious Benedict Society series.

Arthur should be happier than ever. Professor Sherlock Holmes has accepted him into the esteemed Circle of Light, and his friendships are stronger than ever. However, Dinah Grey’s ominous letter and the dangerous secret of her hold over his little sister, Mary, have left Arthur riddled with anxiety. After the annual first-year retreat to the storied Lake District is announced, another letter arrives and makes the key to Mary’s salvation clear: Arthur needs to insert himself in Sherlock’s upcoming investigation…as Dinah’s spy.

While sticking close to Holmes on the trip, Arthur meets George Rankin, one in a long line of protectors of the Brazen Head, a powerful magical relic whose wearer can ask any question and have it answered. But there are more eyes on Sherlock and the relic than just Grey’s. Arthur will have to walk the thin line between truth and deception in order to save his sister, but it might cost him more than he realizes.

• Choosing Between Friends and Family: Arthur loves his found family at Baskerville Hall, but when the villainous Dinah Grey threatens his little sister, Mary, he’s forced to make an impossible choice.
• A Sherlock Holmes Adventure for Kids: Team up with the world’s greatest detective! Arthur must work closer with Professor Holmes than ever before… while secretly spying on his every move.
• Forced Betrayal: To save Mary, Arthur must become a double agent, feeding information about Holmes’s investigation to his greatest enemy. One wrong move could cost him everything.
• Ancient Mysteries: In the mysterious Lake District, Arthur discovers the Brazen Head, a powerful artifact that can answer any question—and everyone wants to get their hands on it.