In the beginning of the movie, we are shown a woman and a man on a date by the pool. Based on their conversation, we learn that they are both lifeguards at the park, and their names are Cindy and Brad. After their shifts end, instead of going home they linger around the premises to spend time together and cozy up on top of the waterslide.
Not long after, a figure carrying a machete comes up to them and brutally murder the two. Some time later, the 2018 graduating class of Valley Hills High School are planning to hold their graduation event. They plan for the event to take place at a water park called Wet Valley.
The idea was spouted by Alice, a Valley Hills High School alumni who was also the one who came up with the entire event. Much like every other graduation event, all the seniors are excited about spending time together. Not only that they’d get to swim and ride water slides, they also plan to stay at the water park for 3 days.
It is now that we get introduced to our protagonist Josh. He and his friends Chad and Slim started a school band called The Blades and they would perform sometime during the event. Later on an old man named Conrad comes up to them.
He tells them that he works as both caretaker and maintenance technician at the water park. Despite having worked there for 35 years, he is still up and kicking. Several hours later, Josh who are in the midst of practicing with his friends happen upon Kim, who apparently is Josh’s ex who now works as a lifeguard.
The small talk shared between Josh and Kim appear to render Kim’s current boyfriend Tommy jealous. Well if you think about it, it pretty much makes sense why he would feel that way given the way his girlfriend came at her ex. In the next scene, we get introduced to Michael who receives a call from his son, Josh the protagonist.
During the call Josh deliberately asks his dad to come to the water park to watch him perform. We then get introduced to one of the people in charge at the park, Priscilla. She is a 1992 graduate of Valley Hills High School.
Slim tells that he heard a rumour circulated among the students about Priscilla supposedly choosing one graduate to have sex with each year. The rest of the class are now enjoying the water park’s main attraction that is a set of really high and long waterslide tunnels. All is good so far and nothing appears out of the ordinary, at least until several bratty teens decide to go down the slide with a bottle of liquor in hand.
The incident prompts Paul the owner of Wet Valley to take action and Conrad the caretaker to clean the pool from broken glass and blood. In the afternoon, Kim and Tommy happen to come across Josh who are hanging out with Chad and Slim. Josh’s friends summon Tommy to ask him to look for a cord extension.
While Tommy get busy setting up the speaker and microphone cables, Josh opts to seize his opportunity to be alone with Kim in another area. Alone and sneaking behind Tommy’s back, Kim and Josh start hooking up. Meanwhile, Josh’s dad is having dinner with Priscilla.
In the beginning, they are shown conversing but we the audience aren’t able to hear what they’re saying at first. Based on their conversation we learn that Priscilla is the wife of Paul, the owner of Wet Valley, while Michael AKA Josh’s dad is known as a wealthy man in the area. During the dinner, Michael voices that Paul doesn’t know that he’s got something good sitting right in front of him.
Some time passes, and now Josh and Kim are walking up to their friends as it is almost time for his band to perform. Several classmates are watching them for afar and one of them says that something is going to happen to them. The seniors are now enjoying a performance by The Blades who are performing 80s hits.
Kim who is watching pretends to not like Josh’s singing and condems the loud noises their instruments make. Josh’s dad and Priscilla attend to watch Josh perform. Up until this point, Tommy is still unaware of the fact that his girlfriend cheated on him.
But then, it turns out that one of the seniors had recorded Josh and Kim hooking up and has now shares the video in the seniors’ group chat. Tommy sees the video and gets understandably furious. He runs up to the stage and beats Josh in front of everyone.
Things escalate even further when Priscilla catches her husband cheating with Alice, the girl in the beginning of the movie. Later on, Michael walks up to his son, Josh, and tries to calm him down. He then asks Josh’s opinion about his idea to purchase the waterpark.
Unbeknownst to them, Alice is eavesdropping and she heard everything. She proceeds to find Paul and reprimands him for negotiating to sell the waterpark. Alice who is Paul’s mistress is insecure as she feels that Paul might leave her after receiving the money he earns from the negotiation.
The drunk Paul assures her that there is no way he would sell the waterpark as it is his only source of income. Several hours after, all the seniors are resting up for the night, and no one is out and about, except for one person who breaks into one of the water slides, to install a pair of large metal blades, arranged in an "X" shape inside. Even worse, on the next day Michael who is walking around surveying the area is apparently being followed by a mysterious figure.
Michael gets shot in the leg and is then taken to the shed. As it turns out the shed also contains Cindy and Brad’s dead bodies AKA the two lifeguards from the beginning of the film. In the next scene, we learn that Tommy has been fired from his job and Kim just dumped him.
Shortly after, Conrad comes up to him, and tells him that Kim no longer cares for him. However Tommy still holds out hope because he loves her. After lunchtime, Conrad the waterpark caretaker runs the water that goes down the water slides.
At this point no one is aware of the metal blades inside one of the slides, meanwhile Priscilla who also works there opts to spend her time hooking up with Slim instead of doing her job. In the afternoon, all the seniors are excited to participate in a fun competition with a $500 prize. They would be split into teams and will compete for the fastest to slide down the waterslides.
Naturally Josh teams up with Chad and Slim. However Slim is still nowhere to be found. They instead see Tommy who suddenly comes up to them despite having been fired from his job.
Tommy tells them that he comes not as an employee but as a visitor now and he is also taking part in the competition. The rest of the seniors don’t seem too fond of the idea and won’t let him join. With Slim still nowhere in sight, Josh and Chad decide to ask Kim to team up with them.
Not long after, Tommy who had nothing better to do than stand around notices something amiss. He takes note of a trail of water leaking out of one of the slides. He also finds remnants of the water slide’s material meaning someone has poked holes at the slide.
While all the seniors are lining up to get to the top of the slides, Conrad is chilling by the pool waiting for the competition to start. While this is going on, Tommy who is now convinces that one of the slides has been tampered with begins trying to discourage everyone from going down the slides. Unfortunately, the seniors brush him off as they already think of him as a party pooper for what he did the other night.
In mere minutes, the competition is about to begin by the event organizers and the pool caretakers. To ensure everything would go well, Priscilla communicates with Conrad who is guarding below. Of course neither are aware of the blades installed inside one of the slides.
Tommy is relentless. He still tries to inform Paul and Priscilla that everyone’s in danger. Unfortunately, nobody believes him, and the competition commences.
One of the annoyed seniors even push Tommy down the slide. At the same time three girls are going down the same slide and as expected, they are instantly mutilated by the blades. Below, the water coming out of slide number 3 has turned red, followed by mutilated limbs sliding down.
The rest of the visitors shriek in horror, while Conrad sprains his ankle while he rushes down his lifeguard seat. Meanwhile, Tommy who was pushed down the slide earlier has now almost reached the metal blades. He has no choice but to cross his fingers and hope nobody else slides down after him.
At the same time Conrad immediately tells Priscilla to stop the competition. And just so happens their walkie talkies are not working properly. Hence Priscilla remains blissfully unaware of the chaos below and instead invites Paul to slide down.
Paul takes the doomed slide number 3. Josh now rushes upstairs and asks everyone to stop going down the slides. Paul who is in the midst of going down the slide proceeds to try to keep from sliding down further.
Meanwhile, the two senior girls and Tommy who are already crammed down the blades get pushed down further and die. Nobody certainly expects that all this fun and games would turn this bloody. Amidst the panic, Conrad asks Chad and Kim to shut down the water pumps in the shed.
But upon entering the shed they stumble upon the dead bodies of Josh’s father Michael along with the two lifeguards. Back to the slides, Paul can no longer hold on due to the rapid rush of water. He slides down and falls victim to the horrific blades as well.
Following the massacre, Josh is informed by a lawyer that his father has left him quite an inheritance. However one thing his father has not yet finalized is the purchase of the Wet Valley Water Park which he had planned to demolish to make space for a 20 million dollar shopping complex. Since Paul the owner died in the incident as well, that makes Priscilla the sole recipient of the money made from the transaction.
The film ends with Priscilla smiling, followed with her memories showing her was killed at this park years ago, with no one was even bothered to help him. She witnessed the entire thing when she was still a girl, and we can conclude that the culprit behind all the 2018 tragedy is Priscilla. She most likely concocted an elaborate plan, perhaps as a form of revenge, and simply to gain an inheritance.
