Magic Treehouse night of the ninjas

Two young children ( Jack and Annie) are looking for their friend Morgan. They have a ninja come into their treehouse and think that he knows where their friend is. They think he is the one who took her so they proceed with caution. They find the master Ninja who explains to them that they are not a threat and help them get back home. At the end of the story they give them one clue to help them find their friend. The book is a good setup for the rest of the stories and creates a lot of suspense. If you are a younger reader and are looking for a series to dive into consider this story.