A tap on the window / Linwood Barclay.

It's been two months since private investigator Cal Weaver's teenage son Scott died in a tragic accident. Ever since, he and his wife have drifted apart, fracturing a once-normal life. Cal is mired in grief, a grief he can't move past. And maybe his grief has clouded his judgment. Because driving home one night, he makes his first big mistake. A girl drenched in rain taps on his car window and asks for a ride as he sits at a stoplight. Even though he knows a fortysomething man picking up a teenage hitchhiker is a fool, he lets her in. She's the same age as Scott, and maybe she can help Cal find the dealer who sold his son the drugs that killed him. After a brief stop at a roadside diner, Cal senses that something's not right with the girl or the situation. But it's too late. He's already involved. Now Cal is drawn into a nightmare of pain and suspicion. Something is horribly wrong in the small town of Griffon in upstate New York. There are too many secrets there, too many lies and cover-ups. And Cal has decided to expose those secrets, one by one. That's his second big mistake.