Claudia Walker wakes up on the beach and can't move her arms or legs. Laying there, she realizes that she's been buried alive in the sand and that no one is nearby. Despite her worries, she finally starts screaming in the hopes that someone will hear her and come help her.
Claudia then flashes back to the day she got an invitation in the mail from her old summer camp friend Marla. She invited Claudia, Joy, and Sophie to spend a week with her in her family's summer home. Claudia recalls Marla picking them up from the train station and starts crying. A random guy suddenly shows up and helps her out of the sand.
She notices that his skin feels a little cold, which he explains away as being from the ocean. He helps her back to the house and hesitates when she asks his name before telling her that it's Daniel. Daniel, for some reason, knows the code to enter the locked gate around the house and helps her inside. When she tries to introduce him to her friends, who claim they didn't know she was still on the beach, he disappears.
When Claudia tells her friends about him over dinner, Marla claims that he's the ghost boy. She says she saw him on the tennis courts once and that he lives in the guest house. Just as they all start freaking out, she reveals it was all a joke. We also meet her butler/servant Alfred when he serves a salad and Joy screams. There was a worm in her lettuce, and she has a massive fear of bugs. Alfred carries it away and serves them hamburgers. Later, Claudia flips out when she thinks that she sees someone in the guest house. Marla convinces her that it was just a trick of the light.
The next morning, Claudia and Marla have some alone time together. Claudia brings up Alison and reveals that Marla's sister Alison died the summer before. Marla gets angry and storms off. Later that same day, they head down to the beach, and Sophie almost gets electrocuted when she grabs the electrified fence and it's still turned on. She's okay, but Marla keeps swearing that it should automatically shut off during the day.
They get a few minutes alone before two random guys show up. Claudia swears that one is Daniel but it isn't. They introduce themselves as Carl and Dean, and they're kind of asses. They start going through their cooler and picnic baskets without permission and basically tell Marla that if she's good, they'll share with her. Joy and Sophie naturally think they are the hottest things ever. Dean also slaps Marla and says he was knocking off a bug before they run off.
Sophie and Joy get super bored that night, and since there aren't many things to do in the area, they decide to go to the boardwalk. Carl and Dean show up, and Joy and Sophia pretty much immediately leave with them. Marla wanders off, and Claudia gets all excited when she sees Daniel and accidentally calls him ghost boy. When he hears her nickname for him, she kind of just laughs it off.
Daniel still feels cold to her touch, but he convinces her that she really needs to get on the ferris wheel with him. When they get close to the top, Daniel leans over the side and falls to his death. This causes Claudia to flashback to what happened the summer before.
Alison was Marla's little sister and a major pain in the ass. Every time she caught them doing something wrong, she told on them. She showed up when they were playing truth or dare and threatened to tell the counselors on them if they didn't let her play. Marla gave her two options: tell them about the time she made out with Marla's boyfriend or walk the log across this massive gorge. Marla stayed behind, while the others went with her. She got halfway across, freaked out, and then they all ran away when the counselors came.
Claudia then comes back to the present day and sees that Daniel is fine. He teases her and says that since he's a ghost, he simply floated away. They flirt some more after getting off the ride and wander around the boardwalk. Just as they find her friends, she turns around and he's gone again. When they get home that night, everyone heads to bed, but Claudia wakes up when she hears Joy screaming.
It turns out that someone sneaked into her room and put leeches on her after she went to sleep. Marla flips out and rushes off to find Alfred. Once she's gone, Joy says that she thinks Marla lured them there to pay them back for what happened to her sister. After everyone finally goes back to bed, Claudia goes downstairs for a glass of water and thinks that she sees Daniel. Alfred pops up long enough to tell her that Marla changed all the codes and that no one other than their group now has access to the house.
The next day, they all go water skiing. Sophie goes first and goes down hard. Marla claims the boat stalled, and since Sophie seems to be drowning, Claudia rushes out to save her. They both get caught in an undertow that drags them out to sea. She passes out and wakes up to find that Dean and Carl came out of nowhere to save them. They then admit that they stole the boat to save them and take off. Joy finds that someone cut the rope Sophie used and once again suggests that something is up with Marla.
Claudia flashes back to what really happened that night last summer. Alison begged them to help her but they still ran away. Claudia could still hear her begging for help. The counselors searched for her the next day but only found her blood stained shirt. The girls briefly wonder if Marla brought them there to torture them before she pops up with chocolates for them.
This next part is cray-cray. Claudia goes for a walk on the beach and thinks she sees Marla. The other girl runs away, and Claudia then realizes that there are literally no animals or birds on the beach. A big ass dog comes out of nowhere and chases her into the ocean. She and the dog fight until she sees a shark coming towards her. Claudia then gets caught in the riptide and pulled out to sea, but she does see the shark attack the dog first.
Claudia wakes up on the beach to see Marla standing over her. Marla says she saw her on the beach and thought she was dead. She helps her back to the house, but Claudia then realizes that the dog that attacked her was Marla's guard dog. When they get back, she runs to get Sophie and Joy, but Joy is out on a date. Marla then comes in and helps take care of her injuries.
When Joy gets back, they pack their things and decide to run away before Marla can stop them. After opening a closet to grab some extra things, they see Marla's body fall out. Though they think it's weird that they saw her earlier and she now looks like she's been dead for a few days, they still run outside. That's when they find that the fence is still active and they can't leave.
They try to find the switch to turn it off and stumble across Marla. Turns out that she's actually Alison. She totally didn't die the summer before. Right before she fell off the log, she saw Marla smiling and laughing at her in the woods. When she came to the next day, she pretended that she had amnesia. She then came to the beach house and killed the real Marla before they arrived. Now she plans to kill all of them for what happened.
Just as she starts pointing a gun at them, Daniel comes rushing out of the dark. He and Alison fight over the gun as lightning strikes and knocks out the power. She gets away and runs towards the fence. Though she knows the power is off, she grabs it right as the generator kicks in. Even though Sophie survived grabbing the fence before, it electrocutes and kills Alison.
Daniel then reveals that he's Alfred's college student son. He didn't want his dad to get fired for having him there so he hid in the guest house. Joy and Sophie agree to go inside and call the cops, and Daniel decides to prove he's not a ghost by grabbing Claudia and kissing her.
Isn't this the exact same plot of Slumber Party, or was it Weekend by Christopher Pike? A bunch of girls spend the weekend together with one sister who survived a fire. In the end, it turns out to be the sister everyone thought was dead bringing them there to enact her revenge.