Imaginary Friend by Stephen Chbosky

Psychological thriller of a preteen boy abducted then found six days later seemingly unharmed, but he gains an imaginary friend that begins to instruct him to build a treehouse. Through a series of events his friends and classmates begin to join or resist his actions, becomes a pretty good story but the payoff was kinda dull even though there were some pretty solid moments in the story. Some folks might get turned off by the heavier than normal elements of Christianity in there, even though it's nothing to people used to it (it drove Reddit reviewers nuts, hence why I added that).

Not bad, but not something that's going to catch fire as a cult classic.