A group of seven high school students has been invited by Bob, the class nerd, to enjoy a weekend of sailing around the Florida Keys. What these seven do not know is that Bob has planned this weekend for many months. He plans to take revenge on these popular kids because he has hated them for years.
In the first scene our hero, quiet and shy Daniel, and our heroine, sweet and pretty Kathy, are talking inside a cabin when a scream brings them running up onto the deck. It is head cheerleader Susie who has cried out.
Bob is holding a gun to her head and is demanding to have a meeting.
"This boat is rigged to sink in a few minutes," Bob says. "There are two lifeboats on board. Both are equipped with small outboard motors. Both are tiny; they will hold only two people, three at most. If you put more people in them, they will sink. In two minutes I am going to head back to shore in one of the lifeboats. I am going alone. That will leave the seven of you to decide who is to live and who is to die. The lifeboat I'm leaving is equipped with a compass and enough gasoline to reach shore. With any luck, whoever departs in it will make it safely back. The hull of this boat is rigged to blow in two places. The seven of you can choose to stay and try to plug these holes. That way, working together, maybe all of you will survive. But the odds will not be in your favor.
Because you cannot survive in these waters for even a few minutes. For the last two hours, while you've all been gossiping and eating, we have been trailing slabs of beef in the water. The blood has attracted a large school of sharks." Bob pauses to smile, to gesture to the surrounding fins. "The beef has only whetted their appetites."
Hearing the setup, football quarterback Todd swears at Bob and rushes him. Calmly, Bob lets go of Susie and shoots Todd in the head. Todd's blood soaks the deck as he dies. Bob shoves the body into the water. While the others look on in horror, the sharks begin to feed.
"Now you only have to decide among the six of you who is to die," Bob says.
From below deck come two sharp explosions. Water begins to pour into the sailboat.
Taking his time, Bob climbs into one of the lifeboats. Smirking, he roars off toward the shore.
Now the tension escalates.
Susie wants to leave in the remaining lifeboat immediately.
Because she is head cheerleader, and homecoming queen to boot, she feels she automatically deserves a place. The others do not agree with her, particularly class valedictorian Randy. It is his belief that the three guys—Carl is the third male—should go in the lifeboat.
They are stronger and the girls—pleasant Mary is the final character—won't be able to stop them from taking it. Carl doesn't agree with this. He is captain of the basketball team and Susie is his girlfriend. While the water gushes in and the boat begins to wobble, Randy and Carl get in a fight. Good guy Daniel has to scream to shut them up.
"Let's at least try to plug up the holes," Daniel says.
"A boat this size will take a few minutes to sink. Maybe if we work together we can stop the water."
They head below as a group, but they are not a cohesive group. They do not trust one another. They cannot concentrate on fixing the holes because they are concentrating solely on each other. It is only now they appreciate the cold cruelty of Bob's revenge upon them.
In a sense, Bob is asking them to destroy one another.
As the water rises to the deck, the opportunity to fix the holes passes and Susie and Randy bolt for the raft.
They are in it and ready to push off through the surrounding fins when Carl jumps in with them. Ironically, he accidentally knocks his girlfriend into the water.
Susie's screams rend the air as the sharks tear her to pieces. Horrified, Carl blames Randy for her death, and the two get into a shoving match. In the end, of course, they both end up falling into the water and get eaten alive.
Now there are only three left: