The trap / Catherine Ryan Howard.

Stranded on a dark road in the middle of the night, a young woman accepts a lift from a passing stranger. It's the nightmare scenario that every girl is warned about, and she knows the dangers all too well - but what other choice does she have? As they drive, she alternates between fear and relief - one moment thinking he is just a good man doing a good thing, the next convinced he's a monster. But when he delivers her safely to her destination, she realizes her fears were unfounded. And her heart sinks. Because a monster is what she's looking for. She'll try again tomorrow night. But will the man who took her sister take the bait?