Newlyweds Mattie and Cole Walker are teaching Cole's daughters how to snowshoe in a remote canyon when a shattering scream pierces the air. They know that somewhere ahead, someone has been injured or worse. Cole takes the girls while Mattie and Robo go deeper into the canyon to search for the source of the scream. From a distance, Mattie and Robo see a shadowy figure at the base of a cliff, but a rockslide buries the person under layers of stone and shale before they can provide help. Desperate to uncover the individual in case they're still alive under the rock, their efforts are in vain. The victim is already dead. When they investigate the canyon rim from which the person fell, they discover evidence that indicates the fall was no accident. To make matters worse, the victim was one of Cole's friends. The Timber Creek County investigative team springs into action, uncovering a trail of greed that leads to a killer who threatens Mattie's cherished new family and tests her with the most difficult task she's faced in her duty as a K-9 handler.