Plot
Universal Bio Tech Research Facility secretly works on enhancing horned viper snakes with poison C12 for their venom to cure disease. The enhanced venom cures a woman of breast cancer. The snakes, however, eventually murder four people. Mr. Staffin subdues the staff and orders his own men to load the snakes. Dr. Akim shoots the glass of the tank, releasing the snakes, before Staffin shoots him with a sleep dart. The snakes kill everybody except Staffin, who escapes.
The snakes rapidly repopulate. Meanwhile, on the island of Eden Cove, a newlywed couple is murdered on a beach. Meanwhile, a young man named Cal Taylor has come to Eden to see Doc Jim Silverton, bringing things from the latter's deceased son Joey. Doc is retiring and Cal may take over for him. Sheriff Tom Hendricks eventually calls Doc, saying that teenager Maggie broke into a store and smoked marihuana. When Doc and Cal get to the store's garden, owner Nicky and Maggie are arguing. Maggie's parents, a man named Jack and his stranged wife Ellie, are also there, arguing.
Outside, a woman named Emily Willis eventually screams. Her child, Jake, was bitten by a snake. Nicky rushes Cal and Jake to the clinic. There, Cal injects Jake with antivenom, stabilizing him. Doc takes Jake to a hospital with Cal subbing in for him, and Nicky is taken to prison for growing marihuana. Meanwhile, Dr. Vera Collins, who works at Universal Bio Tech but only recently learned that the snakes were enhanced, tells Burton that she has a limited supply of C12, which will only immobilize the snakes temporarily. However, C12 will also kill humans. Vera needs to examine Jake's bite and determine if it comes from one of their vipers, and to contain the problem on Eden if so. He then introduces Jon Staffin as his security chief and sends them out. On Eden, Jack drives Maggie back to the inn he owns.
Tom visits Cal at the clinic while he is patching up Ellie, who insists on pressing charges against Nicky for assault. Tom asks if she is overreacting, and Ellie accuses him of having feelings for Nicky, but he denies it. Doc calls Cal, saying that Jake is getting worse, and that the bite had an unusual amount of venom in it, and says that while they have no more antivenom, he will be back in the morning and they should be fine. When they get off the phone, Vera and Staffin ask to speak to Doc. In the inn, Jack and a woman named Georgie have sex. While Jack showers, Georgie is killed by the vipers. Tom takes Cal to examine Nicky, still in prison. Nicky shows remorse about Joey's death and the fight they had before he enlisted and left, ultimately leading to his death. Cal later exits, leaving his tools, which Nicky uses to escape. Local Hank Brownie shows Tom a lake full of half devoured fish carcasses. At the inn, Jack finishes dressing in the restroom and enters the room to find Georgie's body. Cal and Nicky stumble upon Jack in a panic state, and Cal saves Nicky from a viper. They carry Jack's body away because Georgie's body is covered in vipers.
At the lake, Tom finds more vipers, and unknowingly tells everyone to run for the hotel, however Maggie runs the wrong way and does not reach the inn. The snakes intrude the lobby, where everyone is hiding, but Cal scares them off with a fire extinguisher. Against Tom's orders, Ellie leaves to find Maggie. She finds her, but they get surrounded on the bridge. Tom appears and saves Maggie, who cannot walk, and locks her in the safe room at the sheriff's office. The snakes kill Tom, and Jack saves Ellie. They get cornered outside the office, but Cal and Nicky once more use the extinguisher to deter the snakes while they all hide in a van. Cal jumps out of the van and uses the extinguisher while rescuing Maggie and returning to the van, but Cal gets bitten in the process. The van refuses to start and they have to run a café's back entrance, but Ellie gets attacked, and Cal barricades himself, Maggie, and Nicky into the backroom of the cafe using ice, inferring that they do not like the cold. Meanwhile, Doc, Staffin and Vera reach the island and find snakes eating dozens of corpses. En route to the inn, they use grenades of C12 to subdue the snakes. Jack, who is alive, finds Maggie, Nicky and Cal and takes them to the inn also. One of the men with the rescue, Simpson, is killed by a snake, and Vera is repulsed by Staffin's order to move on.
Everyone meets up at the inn, but rescue is not coming until morning. The townspeople are restless and try to leave using the boat Bio Tech arrived on. This leads to a fight in which Jack gets shot. The townspeople leave the inn while Maggie has to be pulled away by Cal. Many are attacked while attemptting to reach the boats. The remainder retreat back to the inn. Jack succumbs to his injuries despite Cal's efforts. The snakes later try to get in. Doc kills one, and they try to barricade the doors. One of Staffin's men, Lewison, cracks and tells the truth, that they were not there to rescue the town, they were sent to gather vipers and take them back, and that aircraft were coming in the morning to gas the entire island, killing everyone left by then.
Cal, Doc, and Vera plan to lure the snakes off the boat, call off the airstrike and escape. Staffin secretly scolds Lewison for revealing plans and reveals that there is a contingency plan. Maggie guides everyone downstairs to where her dad stores a truck, and they attach any heat sources they can to it. Cal tells Maggie to help Doc get to the boats so he can call off the airstrike. Lewison drives the truck while Cal, Staffin, Nicky, Vera and Brownie attract the snakes with heat and guide them to the greenhouse, where Cal plans to trap and kill them. Doc guides the rest of the townspeople to the boats and tries to get ahold of the truck over the walkie talkies, but does not get a response. Maggie takes off but Doc cannot chase after her and departs with the boat. The truck succeeded in guiding the snakes to the greenhouse, and they rush inside. Lewison is bitten, and Maggie appears with more C12 to temporarily subdue the snakes, saving Cal. Vera uses fertilizer and gasoline to create bombs while the snakes weaken the glass until they eventually get in. Staffin gets bitten and, when he dies, they realize he had a radio on him the entire time. He was planning to escape by himself and leave everyone else to die. Vera demands Burton to call the attack off, but he thanks her for her scientific sacrifice and turns his radio off. Cal tries to radio Homeland Security, but they say that Eden is under quarantine and the radio gets jammed by Bio Tech. Brownie accidentally shoots and cracks the glass roof and the snakes begin climbing in, killing Brownie.
Nicky and Vera use flares and propane tanks to ignite the greenhouse, causing an explosion. They see the aircraft coming, but realize that Doc got through when they do not gas the island. Meanwhile, Burton is giving a speech about Bio Tech's profits to interviewers when his walkie talkie conversation with Vera admitting his plan to kill everyone to cover himself is played over the intercom. Burton is arrested. Cal made the recording and was playing it over their speaker system through his computer. Burton is out on bail and gets into a vehicle while on the phone making plans to make everything disappear when he is killed by a snake hiding in his car.
