Monster Island is a horror movie starring a Hollywood star ensemble including Carmen Electra, Mary Elizabeth Winstead and Nick Carter. The storyline starts when a high school senior named Josh unknowingly wins on MTV and gets the chance to see Carmen Electra in person. The contest entry was actually made by Josh's sister, Jen, who was the real winner of the contest. Jen invites their school mates to come with them. Josh and his friends arrive on an isolated island, which is later unraveled to be nested in the Bermuda Triangle, and proceed to have a party. Josh, being recently dumped by his girlfriend, was not really into the party.
As they trek the island, the siblings catch a glimpse of what seems to be a giant flying ant. At first, the two did not believe what they saw and got back to where the concert was being held in. Josh and Jen, being the winners of the contest, received backstage privileges to see the concert star. Josh immediately becomes attracted to Carmen and later on joins the star on the stage. Suddenly, the flying ant that remained an illusion to Josh and Jen's minds appeared right before their very eyes and in front of the entire crowd, instantaneously creating panic. Carmen, alongside her bodyguard Eightball, are grabbed by the insect.
Josh then sees as the flying ant flaps its wings to the direction of a faraway volcano with Carmen still held hostage and her bodyguard dropped off in a nearby forest. Out of fear and shock, the people at the party try to call for help. But to no avail, the signals on their phones were cut off. People begin to board the boats they came in and flee the island. Josh attempts to stop and convince them to look for Carmen, yet fails to do so. Josh's school mates leave for good. He is now left with his two best friends, Andy and Stack, his sister Jen, Lil Mandy, who is a determined reporter, and her cameraman GT. The group was also joined by Josh's ex-girlfriend Maddy along with her new boyfriend Chase, who is also the class' president.
As they venture into the jungle, they are rejoined by Eightball who falls from a tree, dropped off by the flying ant. The group further enters the deepest parts of the island and finds themselves fighting and running from gigantic insects and fish-like creatures.