Off the coast of Alaska, oceanographer Emma MacNeil (Deborah Gibson) is studying the migration patterns of whales aboard an experimental submarine she took without permission from her employer. Meanwhile, a military helicopter drops experimental sonar transmitters into the water, causing a pod of whales to go out of control and start ramming a nearby glacier. In the chaos, the helicopter crashes into the glacier, and the combined damage breaks the glacier open, thawing two hibernating, prehistoric creatures. MacNeil narrowly avoids destruction as, unknown to her, a giant shark and octopus are freed. Some time later, a drilling platform off the coast of Japan is attacked by the octopus, which has tentacles large enough to wrap around the entire structure. After returning to Point Dume, California, MacNeil investigates the corpse of a beached whale covered with many bloody wounds. Her employer Dick Richie (Mark Hengst) believes them to be from a tanker propeller, but MacNeil insists they appear to be from a creature. Later, she extracts what appears to be a shark’s tooth from one of the wounds. Elsewhere, the huge shark leaps tens of thousands of feet into the air from the ocean and attacks a commercial aircraft, forcing it to crash into the water.
Le Méga Shark revient mais il va devoir faire face à un crocodile géant : le Crocosaurus. Attaquant beaucoup d'humains, les deux monstres se battent en duel. L'amiral Calvin et l'agent Hutchinson décident alors d'envoyer le lieutenant Terry McKormick et le chasseur Nigel Putman mettre un terme aux attaques des deux monstres.
After a snowboarder inadvertently starts a major avalanche, the moving snowfield uncovers and wakes a prehistoric "snow shark" which had been trapped beneath. The shark develops an appetite for human flesh and the staff at the Twin Pines Ski Resort begins getting reports of missing people and strange finned creatures moving under the snow. Fearing financial loss on what is their busiest event day of the year, the Bikini Snow Day, the Twin Pines management tries to hide news of the missing skiers and sightings of strange creatures. Disaster strikes as the bikini-clad snow bunnies one-by-one become meals for the shark. The avalanche has cut off the roads trapping all within the Twin Pines Valley. The local sheriff allies with snowboarders to track down the monster.