Dark Ride by Lou Berney

Twenty-one year-old Hardy Reed's life changes the day he sees two children he believes are being abused. Hardy first reports his suspicions to the authorities, but he realizes they are overworked and probably won't do anything in a timely manner. Growing up in foster care and losing his own mother at a young age have made this event particularly hard for Hardy to forget. After Hardy determines that the children's mother, Tracy, and the kids (Pearl and Jack) are all in danger, he decides he must be the one to save them. But is Hardy, a stoner and underachiever, any match for someone who is truly evil? Dark Ride is a tense, unsettling story. For readers of Lee Child, Thomas Perry, and Dennis Lehane.