The film starts off expositing about random stuff that has nothing to do with anything, such as saying there are reports of a new breed of shrew raising from the south and eventually going to Alaska, but the whole story takes place on a remote island off the coast of Texas. The story here features a ship captain and his side-kick landing ashore a remote island whose only inhabitants are a few scientists, a helping hand, and the daughter of the lead scientist. They've come to deliver something or other, but there's an incoming hurricane, and they need to keep the boat locked in place for the night, much to the dismay of the island's inhabitants. We eventually get introduced to the whole crew, and shown what we can only assume is a shrew, a normal one. Everyone keeps acting weird and oddly distant regarding any talk about shrews, save for the one guy that's just oddly fascinated by them. After the captain keeps being persistent in his desire to go check on his boat and swabbie, everyone finally expositions the fact that there are giant shrews on the island that are a mutation of the shrews they were breeding for the purpose of learning how to control overpopulation. Shortly thereafter, the deckhand gets chased by a pack of dogs with rugs tied to them and presumably killed and devoured.

Late into the night, some noises come from the basement and the helping hand at the facility discovers that one of the shrews has dug into the basement. The hand gets the captain, and they make their way into the basement and kill the thing, but the hand gets bitten in the process and dies suddenly. It appears that scientists tried poisoning these giant shrews some time back, but they instead just absorbed the virulent poison into their system, and now anything they bite dies within seconds. With this new found information, it becomes clear they all need to get off the island quickly. In the morning, the captain and one of the scientists go out to try to call in the boat. Along the way, the scientist tries to threaten to kill the captain because he's jealous of the attention the head scientist's daughter is giving him. Clearly, this doesn't work out for him, but they make their way to the shore. However, they discover that the boat is unmanned and, shortly after, discover the remains of the deckhand.

You shrew'd director, you...

Then a pack of dogs with ...er, "giant shrews" come out of the woodwork ...or just woods in this case, and they give chase to the scientist and captain, but the scientist is a coward and leaps into the gates of the island facilities and bars the way so no shrews can get in. Quickly, the others let the captain in, who proceeds to beat the crap out of the coward scientist. Not too long afterward, more dogs with rugs apparently appear in the kitchen in their building, and one of them bites another scientist, leaving only the head scientist, the captain, the daughter, and the coward left. They decide to strap some barrels together and solid-snake it to the beach, but the coward was too scared to come along, staying on the roof. The rest make their way to the beach, getting attacked along the way, but they all make it out okay.