The Treehouse Files Operation

Mr. X is everything you could hope for in a neighbor: kind, friendly, and always ready to lend a helping hand. But sisters Virgie and Lizzie know there's something special about him. He's not just any ordinary neighbor-he's intriguing. With stories from faraway places, a knack for speaking different languages, and an office filled with interesting books and unusual souvenirs, Mr. X is unlike anyone the girls have ever known. After years of wondering about the secrets he might be keeping, Virgie and Lizzie are finally on a mission to discover the truth: is Mr. X a spy, or is he just a regular guy?