Deputy Mattie Cobb and her sister， Julia， travel to Mexico to visit their mother， but when they arrive， they discover that she and her husband have vanished without a trace。 Back in Timber Creek， Mattie finds a chilling note on her front door telling her to look for “him” among the standing dead up in the high country。

The sheriff’s department springs into action and sends a team to the mountains， where Mattie’s K-9 partner， Robo， makes a grisly discovery—a body tied to a dead pine tree。 Mattie is shocked when she realizes she knows the dead man。 And then another note arrives， warning that Mattie’s mother is in desperate straits。 In a last-ditch gambit， Mattie must go deep undercover into a killer’s lair to save her mother—or die trying。