Robert Bridgestone [Kerwin Mathews], a divorced father, takes his son Richie [Scott Sealey] to their mountain cabin for a weekend away from the world. On a moonlit hike through pines and silence, the two are set upon by something dark and predatory. In the fray the mysterious creature plunges down a ravine and is impaled on a wooden fence, yet not before it sinks its teeth into Robert. When they search the scene, the evidence points to a human attacker, not a supernatural monster. The local sheriff, [Robert J. Wilke], dismisses the incident as the work of a deranged drifter, but Richie stubbornly insists that what they faced was a werewolf. His father and the sheriff treat the boy’s belief as childish fantasy, creating a stark gap between Richie’s vivid fear and the adults’ logic.
Sandy Bridgestone [Elaine Devry], Robert’s ex-wife, grows worried about her son’s fixation and begs her ex-husband to consult with the family psychiatrist [George Gaynes]. The doctor weighs the child’s fears and offers a troubling interpretation: Richie’s fixation may be a coping mechanism for the painful truth that his father killed a man. He suggests a counterintuitive plan—return to the cabin the next full moon and allow Richie to witness normalcy there, hoping that the monster fantasy will fade when reality seems unchanged. The idea is to confront the boy with evidence that the nightmare hasn’t followed him, a therapeutic gamble aimed at quieting his imagination rather than indulging it.
Back at the cabin during another full moon, a surge of pain overtakes Robert. He sends Richie to the stream for safety, and in a reflected glimpse he discovers that he has changed into the werewolf he had killed weeks earlier. The sight shocks him into silence, and when Richie witnesses what looks like a resurrection of the beast, he bolts into the woods, fleeing along a mountain road as the creature gives chase. The werewolf’s rampage spills into the road, causing several car crashes and ending with a driver being violently dismembered. Richie stumbles upon a pair of newlyweds camping and clings to them for protection, pleading his case even as the witnesses struggle to believe him. They do agree to help take him home, and by the time they reach the cabin, Robert is nowhere to be found. When he reappears the next morning, he seems dazed and indistinct, leaving Richie unsure how to interpret his father’s strange behavior and mood swings.
The next night, under the full moon, Robert undergoes the transformation again, and the hunt for Richie becomes a tense game of hide and seek inside the house. The werewolf roams the place, and outside, the newlyweds who once sheltered Richie become targets of the creature’s predatory urge, with the beast dragging a camper and leaving a trail of horror in its wake. Richie, still terrified but resolute, discovers that his father is somehow connected to the killings, yet the grownups refuse to connect the dots. When the caravan of danger finally returns to the cabin, Richie learns more directly that his father may be the monster he dreads, a revelation that shakes him to the core.
Richie’s discovery deepens the divide between father and son, and the sheriff’s investigation intensifies. The local doctor’s warnings cannot compete with the raw fear of a child who truly believes his father is a monster. The tension peaks during a visit to the hippie commune on their way back to the cabin. The hippies, led by a wild-eyed figure, form a circle of power and shout at the family to join in. Sandy, driven by a mix of curiosity and caution, partly nods along, but Robert is stopped cold at the circle’s edge as if an invisible barrier holds him back. The encounter hints at a larger, almost mystical force at work, while also underscoring Robert’s fragility in the face of his own suspected curse. A wounded, hopeful Sandy longs for reconciliation, suggesting that perhaps they should try to repair what they once had.
That night, as the full moon rises again, Robert withdraws from Sandy, bending toward the shed where Richie has been preparing, perhaps in search of the truth. Inside, Richie uncovers a bag that confirms the darkest fear—his father has a double life he cannot escape. Robert begs his son to lock him in the shed, a desperate plea to contain the nightmare he has become. When Sandy arrives and the truth spills out, she learns the horrifying possibility that her husband’s transformation is real and personal. The shed door shakes, and a clawed hand appears as danger looms. The family flees to the safety of the camper just as the werewolf launches a final assault on those nearby, including the hippie camp, while the sun seems ready to end the nightmare.
The sheriff’s party stabilizes the scene, but the truth remains chilling: the man who was once a father has become an unstoppable predator during the full moon, and the people around him cannot fully accept the terrible possibility. As night deepens, Richie makes a life-altering decision to intervene and save his father, even as others call for restraint. The mob closes in, firing at the advancing beast, but bullets fail to pierce the creature’s hide. In a moment of tragic resolve, the werewolf stumbles onto a broken stake that once held a hippies’ cross, and the stake pierces its heart. The transformation back to Robert is swift and painful, and the horrifying clarity settles over the scene: the man Richie has always known as his father is now gone, replaced by the monstrous form that nearly destroyed them all. The last image is Sandy, pale and horrified, examining her son’s bite mark and grappling with the terrifying possibility that Richie could inherit the same curse.
