In the middle of the sea, an earthquake shakes the bottom with such strength that it causes a fissure and emits a bright blue light. On the surface, a couple is enjoying their time together when the guy surprises his girlfriend with a proposal. Before she can reply, suddenly something something pulls the man underwater.
The woman is confused as she looks around, only to start screaming when his dead body floats up to the surface. Soon the killer appears too: it’s an alpha zombie, who immediately kills the woman. Meanwhile Hunter, Ray, and his niece Jada are having fun fishing when they see another boat catching fire in the distance.
They immediately rush over and Hunter helps to put out the flames before anything serious can happen. The fire was started by mishandled fireworks, which Hunter confiscates because he’s the local supervisor. He also scolds the group in the boat for drinking and sailing, but Blaine doesn’t take it well.
Meanwhile on top of a cliff, a mysterious man watches the blue light with his binoculars. Back to Hunter’s group, they go back to fishing and Ray catches something quite big on his line. After some effort, he pulls it out and is shocked to see a dead person’s body looking completely blue.
Jada uses an underwater camera to investigate and discovers the blue light on the seabed, which isn’t normal at all. Hunter quickly informs the authorities on the radio and while Jada covers the body, the guys notice the blue light on the surface too. Jada looks away for one second and discovers the body is gone.
This guy is also a zombie and quickly attacks her, severely injuring her shoulder. Ray rushes to distract the creature while Hunter retrieves his machete, stabbing the zombie until it goes down. However the monster soon recovers, so Hunter and Ray team up to push him into the ocean.
In town, Hunter’s girlfriend Kenzie and her daughter Sam receive a call from Hunter, who wants Kenzie to help Jada because she’s a doctor. Kenzie quickly leaves to meet her husband while Sam stays with her friends to attend a concert. Sam meets the singer Dag and sparks fly between them.
Soon Kenzie and an ambulance pick up Jada and take her to the hospital, where she’s checked on by the doctors while Ray keeps her company. In the meantime Hunter meets with Sheriff Akoni and they agree to investigate the strange incident together. They take Hunter’s boat and can already see the blue light on the surface.
Hunter sends the camera again and discovers a wreck with a crack that is emitting the mysterious light. The ship doesn’t have the plaque with name and designations, which is also strange. Nearby, there’s a weird being swimming around.
Hunter says the attacks may be coming from zombies and shares his experience, but Akoni laughs at the idea. At that moment, a big horde of zombies appears in the water and starts swimming toward them, so Akoni now believes Hunter’s story. While Hunter calls Kenzie to tell her to isolate Jada, Hunter calls for help and tells his colleagues to evacuate everyone in the area.
The tsunami siren stars wailing on the beach and people stare in shock at the sea as they notice the water moving backwards. Hunter and Akoni wants to go back to help the civilians, however they freeze when they see a huge wave full of zombies behind them. As people panic about the incoming tsunami, Hunter tries to get the boat going as fast as possible but it still gets caught in the wave and the guys have no choice but to hide.
In just a few seconds, the zombie tsunami reaches the shore and absolutely destroys the area, leaving zombie bodies on every corner. Hunter and Akoni make it safely to the shore too and Akoni pulls out his gun on a zombie, but he decides to save bullets for now. At the hospital, Kenzie informs Ray that most of the staff has been evacuated so Jada won’t be seen for a while, meaning she and Ray will have to stay in quarantine for now.
Back on the beach, there are quite a few survivors, so Hunter and Akoni try to warn them of the danger. However it’s too late: the zombies that crashed with the wave are waking up and more are coming out of the sea to attack every person they can reach. Most survivors end up becoming zombies too, making the horde even bigger.
Akoni and Hunter use their gun and machete to kill a few zombies, however there are too many of them and people keep on getting killed. Hunter finds a boat and uses the engine to kill a bunch of monsters at the same time, allowing a group of people to escape. Meanwhile Sam and her friends see the attack from a building and they try to call their parents, but everyone is too busy panicking to answer the phone.
At the hospital, Jada wakes up only to die a second later. She immediately awakens again as a zombie and tries attacking Ray, but at that moment a doctor comes in and Jada jumps to bite him instead. Ray uses the chance to quickly run out of the room.
Back to the beach, Akoni kills another zombie with an umbrella. No matter how many they kill though, the numbers keep on growing and the wounded zombies continue to move, so Akoni and Hunter decide to run away and get reinforcements. When they get in the truck, they suddenly scream at a presence in the back, but it’s just Blaine and his girlfriend hiding.
The guys agree to help them and the truck takes off. In the meantime, the mysterious binocular guy reaches the beach and approaches a zombie with a crowbar in hand. In the hospital, Kenzie comes out of a room and is horrified to discover Jada has killed her whole staff.
Jada starts chasing her and when Kenzie runs through the corridor, Ray pulls her into a room and locks the door, which Jada starts pounding on. Unfortunately the staff soon also turns into zombies and helps Jada push until they finally manage to break in, so Ray and Kenzie have to start running again. They make it to another section of the hospital and find a zombie on a wheelchair, not to mention Jada is still following them.
The duo has to keep on running and find a way to escape. Minutes later, Akoni and the others reach the police station and run as fast as possible when they see more zombies coming. The monsters almost reach Blaine, so he pushes his girlfriend towards the horde as bait and joins the other inside.
While the zombies pound on the windows, Hunter calls Blaine out for what he did, causing Blaine to snap and take a gun from an officer. He demands to have the weapons from the armory and when the others refuse, he shoots the officer. Then Blaine tries to run to the armory, so Hunter quickly knocks him out.
Back to Sam and her friends, they leave the building and start running through the streets. They have to push away a zombie and the horde turns onto another running group, bringing down a few of their members. A few blocks later, Sam’s group decides to hide in a market, but this place is full of zombies as well.
Dag trips and hurts his ankle so Sam has to help him walk. The other guy immediately is killed and the group splits: Taani pushes a few zombies off before rushing outside while Sam and Dag run to the back. At the police station, Akoni keeps on trying to radio for help, but nobody answers.
Then Akoni takes an envelope from a safe that says “Revok Pharmaceuticals” and shreds it while Hunter isn’t looking. Speaking of Hunter, he logs into the maritime registry and finds the ship they saw at the bottom of the sea. It’s registered under Revok Industries and its status says “salvaged and junked”, which means the company hid the wreckage.
At that moment the zombies finally break the windows, so Hunter and Akoni go to the armory to grab weapons. Hunter is more interested in the confiscated objects and gets a cool sword with a double blade. On their way out, a handcuffed Blaine asks them to take him too, but they ignore him.
Using police shields, the duo pushes their way through the horde at the door and while Akoni shoots the closest ones, Hunter uses a bazooka to finish off the group coming from the street. Unfortunately the zombies are still moving and to make matters worse, a second zombie tsunami is approaching. The duo escapes on the truck and as they drive through the woods they encounter the alpha zombie so they drive over him.
However the monster is just fine. Back to Sam and Dag, they make it to the parking lot and find his van, where a band member is chilling. He’s had the headphones on all along and didn’t know what was happening.
The guy opens the van for the others before he tries to be a hero, but he can’t fight some many zombies at the same time and is quickly killed. Sam and Dag lock the doors and try to escape, but the van won’t start. Meanwhile Taani manages to leave town and runs through the woods as the zombies still follow her.
She sees a house in the distance and rushes to the front gate, where Marty sees her on the security cameras. This is the mysterious guy from earlier, who has captured a zombie and keeps it hidden in the basement to study it. Marty asks her to show the back of her head to confirm she wasn’t bitten and finally opens the gate when he sees she’s clean.
Taani rushes inside right before the zombies reach her, but now the horde waits in front of the gate. Then Taani borrows Marty’s radio and calls her dad, who turns out to be Akoni. She promises to stay inside with Marty and asks Akoni to get Sam at the market.
At the police station, Blaine manages to reach the body of the dead officer and grabs the keys to finally free himself. When he tries to leave, he finds his zombie girlfriend at the door, who immediately jumps on him and bites him. In the parking lot, Dag admits that he’s been slowing Sam down and tells her to leave without him.
Then he gets out of the car through the window and climbs to the roof, where he starts singing with his ukelele to keep the zombies distracted. At that moment Akoni and Hunter arrive, so Sam runs towards them while Akoni shoots down any monster that tries to grab her. As Sam leaves with the men, the zombies finally reach Dag and kill him.
Afterward the group heads to the hospital, closing the door right before the zombies can reach them. Kenzie isn’t answering any messages, so Sam runs through a corridor to grab a phone before hiding in a room. She uses it to talk through the speakers, asking her mom to find them at the second floor.
The noise attracts a bunch of zombies so Hunter and Akoni start fighting them with a gun and the fire extinguisher. Sam doesn’t realize that the phone cord is stuck around her leg, and soon the monsters start pulling it from outside. A zombie breaks the door with its head so Sam has to defend herself with the double blade.
At the same time Hunter grabs two wires from the power box and electrocutes a zombie, which starts an electricity chain that jumps from creature to creature and kills them all. Then Kenzie and Ray arrive in the elevator. A zombie gets in Kenzie’s way, so she quickly punches it down and finally reunites with her daughter while the guys lock the zombie up.
The group starts making their way out and Kenzie notices that the zombies that came with the wave look different from those who were turned with a bite. She concludes those people were experimented on. Outside, Hunter brings down a few more zombies with the blade so the group can get on the truck and finally escape.
Moments later they make it to Marty’s house and Taani gets to reunite with her dad. She notices that Akoni has a wound and Marty freaks out, but Akoni assures them it’s just a scratch and he wasn’t actually bitten. Once everyone is inside, Akoni uses Marty’s radio to try to ask for backup, although Marty says he hasn’t been able to contact anyone since this all started.
Taani realizes that they had two tsunamis and nobody has come to check the area, which means there’s some conspiracy behind it. At that moment, the zombie prisoner breaks free from its chains as it growls. Akoni hears a noise and goes to investigate, entering the experiment room and finding the bed empty.
Suddenly the zombie jumps on him and after some struggle, Akoni gets bitten. As he yells in pain, he kicks the zombie off him and the noise of the monster hitting the furniture alerts the others. The zombie hears them and goes upstairs, where the guys push it away and it ends up fighting against Kenzie.
Marty immediately attacks it with his taser, instantly killing him. Ray brings Akoni upstairs and Taani takes care of his wound while Hunter connects the taser to the blade to make a more effective weapon. The group scolds Marty for hiding a zombie, so he explains he’s been experimenting to learn their weakness.
These zombies are full of a liquid with phosphorus, which explains the glow in the water and why electricity is the only way to truly stop them. Hunter concludes they must lure the zombies back to the water and run power to it to kill them all at the same time. They will also have to blow the wreckage so it can’t make any more monsters, so Marty reveals he has a huge supply of grenades and C4.
While the group starts packing up the weapons, Hunter goes outside to clear the way but the taser doesn’t work. The gate suddenly opens so Kenzie comes out to help as well. She turns on the wood chipper, then she and Hunter begin fighting the zombies to throw them one by one into the chipper to obliterate them.
Their teamwork is perfect and soon all the enemies are killed so the group can escape. On their way out, Kenzie tells Hunter that if anything happens to her, he should take care of Sam. Akoni soon starts feeling sick so they stop to rest in a cave.
It’s strange that he hasn’t turned yet, and Marty explains that he wasn’t bitten near his head so the infection is taking longer to reach his brain. Knowing that the end is coming, Akoni decides to confess what he knows. Thirty years ago, a pharmaceutical company came to this beach to test a new anti-aging medicine in a ship away from government scrutiny.
They bribed everyone to keep the secret, including the local council leaders. Akoni agreed to help because they promised to provide his wife with medical care, but sadly she died anyway. However the medicine wasn’t actually ready for human trials and caused terrible side effects, so the company shipped out the patients and the staff before sinking the ship with the infected people inside.
They also removed the identification plaque because it had the company logo on it. Kenzie suspects those weren’t side effects and that making weapons out of humans was the company’s intentions all along. At that moment the zombies find them and attack.
Hunter finally makes the taser blade work and starts killing the creatures with Marty’s help while the others run away. On the way out, Taani must leave Akoni because he finally dies, but she makes sure to put a grenade in his hand. Once all the zombies are down, Hunter and Marty join the others and get out of the cave.
Before leaving, Taani watches how Akoni wakes up as a zombie and in his last seconds of clarity, he activates the grenade. The explosion blocks the cave and stops more zombies from following them. Moments later the group makes it to the beach and splits to carry on the plan.
Marty also reveals he left some C4 in his house and uses a remote to blow it up now. Ray, Marty, and Taani leave on a boat to take the C4 to the wreckage. Marty is making all the connections and Taani tells him to hurry because the zombies are swimming towards them.
Hunter takes some wires and drags them to the tidal pools while Kenzie and Sam wait by the power box for the right moment to activate the electricity. Then Hunter takes a bike and plays some loud music so the zombies start following him to the beach. At that moment Marty jumps in the water to install the C4 and is surrounded by zombies.
Ray wants to help him, but a zombie also comes aboard and blocks the way. By the time Taani pushes the creature off, it’s too late and Marty has already been killed. When Hunter is about to make it to the pools, the vehicle gets stuck in the sand and he has to continue on foot.
Suddenly he’s found by the alpha zombie, who pushes him to the ground. The taser in the blade is failing again, so Hunter has to fight him with normal hand-to-hand. The alpha zombie immediately disarms him and grabs his wrists, thus Hunter kicks him a few times to get him off.
Kenzie sees all this and rushes to get the bike unstuck, playing the music again to finally guide all the zombies to the tide pools. Hunter continues to fight the alpha zombie and when he gets grabbed by the neck, he uses the chance to take out a hidden knife and cut off the zombie’s arm. At the boat, Taani continues to shoot the zombies that try to get aboard but they just keep on coming.
Ray gives her a life jacket and tells her to escape as her dad would’ve wanted, so she jumps into the sea. The alpha is still fighting Hunter, who kicks him before retrieving the blade. The taser finally works and he manages to cut the zombie’s head off, kicking him into the pool at the same time that Sam finally gets the power box to work, electrocuting all the zombies in one go.
Once Taani has swum far enough, Ray says goodbye to Hunter through the radio and activates the C4, dying in the resulting explosion. A huge wave forms and begins approaching the beach, so Hunter has to run away. He finds his way blocked by a zombified Blaine and takes great pleasure into stabbing him with the blade, making his head explode.
Then Hunter manages to escape right before the wave hits the shore. He reunites with Kenzie and Same, who are helping Taani out of the water. The couple kisses and the family watches the coast guard ship coming in the distance.
