Trouble is a Friend of Mine by Stephanie Tromly

From the moment Phillip Digby first appears on Zoe's porch, he will not leave her alone. Digby pops up at any moment and seems to know way too much about what is going on. It's kind of creepy and yet Zoe is drawn into his schemes even when she is breaking the rules.

And breaking the rules will not get Zoe into Princeton. Her goal is to get into the exclusive Prentiss Academy in New York first. Since her parents are separated, she will move in with her father and his new wife in New York (which her mom is not thrilled about).

After the divorce, Zoe and her mother moved to River Heights, a small town still reeling from the abduction of a local teen. Digby's mission is to find the girl or at least the person (or persons) who did it. It's just possible that this kidnapping may be connected to the disappearance of his own sister eight years ago.

Digby drags Zoe and his friend Henry through a series of investigative adventures: stakeouts, break-ins, interrogations, vandalism - you know, general mayhem that eventually involves the police.

Zoe keeps following Digby because she has no other friends and he at least gives her something to do. Plus Digby is smart and has studied police methods and procedures. He is passionate about finding this missing girl. It's suspenseful, a bit chaotic and fun.

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