Like the last Dinosaur Drive-In film
The film opens with a trio of scientists who have discovered a cave painting—said to be thousands of years old but looking like it was made with a Sharpie just yesterday—depicting Native Americans attacking a plesiosaur. The scientists have to scramble out of the cave as the meteorite strikes the lake, and they soon forget their first discovery to investigate the impact. Pretty standard monster movie stuff, but the movie jumps the track when we meet our unexpected protagonists, a pair of local ne'er do-wells named Arnie and Mitch.
Arnie and Mitch are meant to be the film's comic relief. They are not the least bit funny. They haggle, squabble and complain for an inordinate amount of time without moving the plot forward, outside perhaps of giving people an opportunity to fall prey to the lake's plesiosaur by renting them boats. After finding one of their rented boats full of blood and a snooty couple in shock after a run-in with the monster, Arnie and Mitch begin to suspect something might be up, though they never see the monster themselves despite working around the lake, scuffling in the lake and otherwise acting like oblivious potential prey items. Perhaps the odd day-night cycle is responsible for their weird behavior. Throughout the movie characters keep saying things like, "look at all the stars," in the middle of the day; the director apparently tries to convince his audience that it's dark out by having characters repeatedly comment on it being nighttime, all evidence to the contrary.
In any case, the monster continues to select morsels from the lakeside buffet—from cattle to fugitive liquor store robbers—before running into the town's sheriff. Everything comes together, but when the local law enforcement brings up the problem to the scientists we met at the beginning of the film he receives little sympathy. The researchers basically yell "SCIENCE!" at the sheriff and decide that it would be wiser to trap the monster in a nearby bay for study rather than destroy it outright. A town meeting—filled with people apparently given $5 by the director to be in the movie and giving him his money's worth—is called to resolve the issue, but it doesn't get very far before the monster starts tossing around hay bales in a nearby work yard. It's the last straw for the sheriff, who powers up a flimsy bulldozer that looks capable of giving the monster a very dull shave. Before he can dispatch the monster, though, the plesiosaur kills Arnie, leaving a sullen Mitch alone as the end credits begin to roll. As the yellow list began to flash over the screen, my wife said it best when she said, "wow. Nothing happened in that movie."