Plot

A rescue mission to the bottom of the ocean is terrorized by a massive prehistoric shark.

Five years ago, expert sea diver and Naval Captain Jonas Taylor encountered an unknown danger in the unexplored recesses of the Mariana Trench that forced him to abort his mission and abandon half his crew. Though the tragic incident earned him a dismissal from service, what ultimately cost him his career, his marriage and any semblance of honor was his unsupported and incredulous claims of what caused it - an attack on his vessel by a mammoth, 70-foot sea creature, believed to be extinct for more than a million years. But when a submersible lies sunk and disabled at the bottom of the ocean - carrying his ex-wife among the team onboard - he is the one who gets the call. Whether a shot at redemption or a suicide mission, Jonas must confront his fears and risk his own life and the lives of everyone trapped below on a single question: Could the Carcharodon Megalodon - the largest marine predator that ever existed - still be alive - and on the hunt?—Warner Brothers

Five years after the catastrophic Philippine Incident that cost him everything, veteran deep-sea rescue diver Jonas Taylor reluctantly picks up where he left off: the dark depths of the notorious Mariana Trench. And as an unknown underwater beast traps three research facility scientists inside a crippled submersible, Jonas must put his expertise to good use to prevent the inevitable and redeem himself. But he is fighting a losing battle: the vicious subaquatic monster circles in on them, hungry for flesh. Is the myth of the horrific Megalodon, the predator that ruled the seas 10 million years ago, real?—Nick Riganas

A rescue team led by Jonas Taylor (Jason Statham) is saving a group of sailors trapped inside a sunken nuclear submarine when Jonas sees the hull of the submarine being damaged by an unknown creature. Two rescuers are stuck in the damaged submarine and say their return to the rescue submersible will take a few minutes. Taylor leaves them behind as he is afraid, they will all die if they wait. As they leave, the damaged sub explodes. Taylor's claim is that a giant sea creature caused the disaster. He is dismissed by his teammate Dr. Heller (Robert Taylor), who believes Taylor was affected with pressure-induced psychosis and blames him for the loss of their friends.

Five years later, billionaire Jack Morris (Rainn Wilson) meets Dr. Minway Zhang (Winston Chao) at the underwater research facility "Mana One", which Morris finances. Zhang and his daughter, Suyin (Li Bingbing), an oceanographer, are supervising a mission to explore what may be a deeper section of the Mariana trench, concealed by a Thermocline cloud of hydrogen sulfide. The mission is being conducted by Lori (Jessica McNamee, Taylor's ex-wife), Toshi (Masi Oka), and The Wall (Olafur Darri Olafsson) in a submersible. The mission appears to be going well until a very large creature hits the submersible, causing it to lose contact with Mana One.

James "Mac" Mackreides (Cliff Curtis), another crew member at the station, suggests sending Taylor down to attempt a rescue, citing the similarity to his story. Despite Heller's objections, Zhang and Mac decide to travel to Thailand to recruit Taylor anyway. Suyin attempts the rescue herself after receiving a signal from submersible, but a colossal squid intervenes. Before it can destroy her craft, a massive shark appears and kills it.

Agreeing to help, Taylor reaches the trapped submersible, saving Lori and The Wall. However, when the giant shark returns, Toshi sacrifices himself by closing the hatch door and detaching the rescue vessel. But before he did that, Toshi makes sure that the letter to his wife will be given by putting it inside The Wall's pocket. This allows Taylor, Lori, and The Wall to escape safely while he diverts the shark's attention to his sub, causing it to be driven into a thermal vent, causing an explosion.

Back at Mana One, the crew discovers that the shark is a Megalodon, the largest shark ever known, believed to be extinct for millions of years. Meanwhile, Suyin's daughter, Meiying (Sophia Cai), goes to the large glass leading to a beautiful underwater view of the ocean, and sees the Megalodon through the glass, and is petrified. When Suyin comes down with Taylor and Curtis, they realize a mother whale was eaten alive by the massive shark which then devours it's distressed pup in front of them.

The crew then realize that it has escaped from the depths of the trench by swimming through a hole in the Thermocline created by the thermal vent explosion, briefly raising the temperature enough for it to safely pass. The group decides to track and poison the Megalodon, which they succeed in doing. While injecting the Megalodon with Etorphine, Suyin's oxygen mask gets compromised, but Taylor revives her with CPR.

Despite initial success, Taylor comments that the teeth don't match up with the previous attack. Shortly after, a second, more colossal Megalodon emerges from the water, devours The Wall and the smaller Megalodon, and capsizes the boat. It also devours Heller, who saves another crew member, Jaxx's (Ruby Rose) life by luring it to himself. The surviving crew returns to Mana One in two dinghies, but Zhang succumbs and dies of injuries caused by the bigger Megalodon's attack. Morris announces that he has informed local governments and naval forces, but it is out of their hands. He dismisses the whole crew and advises them to evacuate in the morning.

At nightfall, Morris attempts to destroy the Megalodon himself by ordering a helicopter crew to drop modified depth charges at it, citing that the creature's actions could result in lawsuits. He approaches the carcass of the supposed Megalodon in a boat but discovers it's a whale. When the Megalodon approaches, the boat accelerates, causing Morris to fall overboard and be eaten by the Megalodon. Taylor and the remaining Mana One crew discover Morris' deception and resolve to track and kill the shark, realizing that it is en route to a crowded beach on the Sanya Bay.

The Megalodon kills several beach-goers before the Mana One crew plays audio of a whale call to divert the shark's attention towards them. Taylor and Suyin attempt to destroy the Megalodon with rigged torpedoes, to no avail, and in the process, Taylor's submersible is severely damaged. Taylor manages to cut the Megalodon with parts of his sub and stab it in the eye with a harpoon. Due to the presence of blood, multiple sharks in the area notice the blood and devour the Megalodon, killing it. During the fight, Suyin was able to evacuate everyone to a boat where a couple is getting married. Taylor gets on the boat, and he and Suyin consider taking a vacation to celebrate their triumph.