The plot focuses on a field trip by Professor Ernst Prell to investigate Yeti sightings, along with four graduate students: Keith Henshaw, Karen Hunter, Tom Nash and Lynn Kelly.
The night before the trip, the professor invites Keith to dinner at a restaurant, where he samples an exotic dish named "gin sung." The rest of Dr. Prell's students attend an off-campus party where they encounter a former student, turned alcoholic groundskeeper, named Spencer St. Clair, who is there with his wife April. St. Clair proceeds to tell everyone within earshot the story of Prell's last Yeti-seeking field trip, which only he and the professor survived.
After the party, Spencer continues to drink, and upon returning home fights with his wife and cuts her throat with an electric carving knife. Afterwards, he climbs into the bathtub fully clothed. He is killed by his not quite dead wife, who drags a toaster into the bathroom and dumps it into the bath, electrocuting him.
In the morning, the professor travels by van with his students to Boot Island, where his friend Dr. Karl Werner lives. Werner has recently seen the Yeti on his island, and conjectures that he was marooned there by melting winter ice. He introduces the others to a mute Native American manservant named Laughing Crow. The group have dinner, which is again "gin sung," then go to sleep after one of the students, Tom, sings a song about the Yeti.
The next day, the professor and his students begin their search in the woods of the island. Tom sneaks off to go hunting and is killed by the Yeti. The rest of the group look for Tom the next morning. Karen finds only his rifle and his severed leg. Meanwhile, Lynn goes into Dr. Werner's greenhouse and sees something that frightens her; she runs into the woods and is also killed by the Yeti.
At the house, the remaining students find that the phone is out of order. The professor decides to use Tom's leg as bait to lure the Yeti into a trap. The plan fails, however, as Prell returns to the house claiming he was knocked down by the monster, who escapes with the leg in its jaws. Prell then decides to try again, using Lynn's body as bait. Karen tries to hide the body in the greenhouse, where she discovers the rest of Tom's body, and passes out. When she awakes, Dr. Prell tells her it must have been a dream as she was asleep for quite some time. Karen doesn't believe him, leading them all back to the greenhouse where they uncover Lynn's body.
Disgusted that Dr. Prell is going to use their friend's body as bait, Karen reluctantly agrees to help out by taking photos, under the condition that they leave Boot Island whether they succeed or fail. Both Dr. Prell and Keith agree, and Karl wishes them good luck.
The professor ties Lynn's body to a tree and the trap is set. The Yeti appears and Keith chases it into the woods. He tracks it by the sound of its heartbeat, but makes the discovery that the sound is actually coming from a speaker attached to a tree. Someone knocks him out with a branch.
Back at the house, Laughing Crow is shown listening to an LP record of the Yeti's heartbeat. It turns out that Dr. Prell and Werner are cannibals, using the Yeti scam as a way to lure victims, and that the Yeti is actually Dr. Werner in disguise. While Karen is asleep upstairs, Keith returns to the house and discovers Dr. Prell and Dr. Werner discussing what to do with her. Werner thinks they should just kill her, but Prell says that the code calls for no body bruises and that she must be frightened to death. Keith pulls out a rifle and orders both men to put their hands up. They ignore him.
He shoots at them, finding out that the shells are blanks. He is then knocked unconscious by Laughing Crow. Still asleep upstairs, Karen wakes to a growling noise. She looks out the window and finds the Yeti running full speed at the house. Karen flees through the house and ends up trapped in a bathroom. She opens a cabinet to find Laughing Crow holding a knife, and dies of fright.
While setting up for their big breakfast, Keith wakes up and manages to sneak away. He tries to escape in the van, but it gets stuck in the mud while he tries to hide from the party guests' funeral procession. Keith then hoofs it down to the bridge where he manages to flag down a cop who takes him back to the house.
At the breakfast, Prell and Werner salute the party guests and hosts, toasting the previous schemes which have provided victims. Keith returns with the policeman, only to find out that he too is a cannibal. Prell and Werner explain that the "gin sung" Keith has eaten is actually human flesh, and they invite him to join their cannibalistic society. They bring in Karen's body, and Laughing Crow, brandishing an electric carving knife, speaks for the first time, saying "Mr. Henshaw — white meat or dark?" Keith drools as the film ends.
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