Deadfall by Stephen Wallenfels

Twin brothers Ty and Cory Bic are on the run. When they encounter a dying deer in the middle of a remote mountain road with fresh tire tracks swerving down into a ravine, they know they have to help. But when they reach the wrecked car the vehicle appears empty, with signs that the driver escaped.

Until they hear a sound coming from the trunk.

Ty and Cory are escaping demons of their own. But what they discover in the trunk puts them in the crosshairs of something darker and more sinister than their wildest nightmares.