Matt, a recently-retired history teacher, finds the mangled corpse of a dog belonging to his neighbors, Lisa and Keith, in his yard and calls Keith, a local police officer and former student he considers a surrogate son. When he finds Detlev Meyer, an assertive young officer investigating the animal mutilations, lurking on his porch he’s struck by his resemblance to his best friend, killed in Vietnam. Det misreads his reaction and becomes suspicious.
The report of a chupacabra (goat sucker) jumping from a tree on the corner of Matt’s yard brings Det back with accusations, and their relationship grows more contentious. Matt suspects the ambitious young officer is hostile toward Latino immigrants moving into their neighborhood in Arden, a suburb of Dallas.
The naked body of a young Latino male is found on a nearby vacant lot, and Matt is pulled into the investigation when Lisa confides that Det suspects him. At a backyard cookout he recognizes Det as the son of an arrogant engineer, who sent the troubled boy to a military academy, and begins to understand him.
Matt sees the chupacabra, which he recognizes as a hoax probably intended to terrify credulous Latinos. He submits a report to Det, who is rudely skeptical, and he exposes a wound sustained in Cambodia. Det discovers his background as a Marine intelligence officer and apologizes, eager to use his skills.
Matt finds a third nude corpse, with vampire-like bites on his throat and a taunting note of his chest, and joins the two officers in pursuit of the killer.