Plot
Five years after the events of the first film, Jonas Taylor has been involved in fighting environmental crimes while helping Mana One explore the Mariana Trench, where the Megalodon had been found. Following the death of Jonas' wife Suyin Zhang, he has been raising her teenage daughter Meiying alongside her uncle, Suyin's brother, Jiuming Zhang, who acquired his father's company with financial backing from wealthy industrialist Hillary Driscoll. Mana One has been studying an 80 ft (24 m) female Meg called Haiqi who was discovered as a pup and trained by Jiuming in a reserve in Hainan.
Jonas and Jiuming lead a routine submersible exploration to the Trench. Fellow Meg survivors DJ and Mac observe them from Mana One. On the way down, the subs are pursued by Haiqi, who escaped captivity the previous night. The subs dive through the thermocline in an attempt to escape but Haiqi forces her way down through it anyway. Down below, they encounter two much larger Megs, a massive alpha male and a beta male, who mate with Haiqi. Jiuming realizes that Haiqi had been acting strange because it is mating season; she was calling the other Megs to mate. Venturing further down, the team stumbles across an illegal oceanic mining operation captained by mercenary Montes, who has a vendetta against Jonas for his imprisonment some time before. Montes' crew was hired by the corrupt Driscoll to use Mana One's access to the Trench to mine rare-earth minerals that could earn them billions. Montes kills his crew in an explosion to cover up their activities, which causes a rupture in the Trench and grounds the team's ships.
DJ, Mac, and Mana One analyst Jess discover that the rescue pod has been sabotaged, forcing the crew to use exosuits to walk toward Montes' station, with only four of them surviving the journey. Jess reveals herself as a traitor and attempts to remotely kill the four, but they escape in a submersible. As the crew surfaces, they discover that the rupture from earlier has caused several Trench creatures, including the three Megs, lizard-like creatures known as Snappers and a giant octopus to escape to the surface.
Jess is devoured by a Meg; Jonas’ team escapes to a nearby resort, Fun Island. Driscoll, Montes, and the mercenaries arrive at Fun Island to kill Jonas' crew, but are attacked by the Snappers, who eat Driscoll. As the Megs and octopus attack, Jonas kills the beta Meg and knocks Montes into the mouth of the alpha Meg to be eaten when Montes attacks him.
Jiuming injures the octopus, attracting Haiqi, who kills the octopus. Jonas uses a helicopter rotor from Driscoll's crashed helicopter to fatally impale the alpha Meg. Haiqi heads towards Jonas, Jiuming, and Mac, but Jiuming uses his training signals to redirect her. As the group celebrates their survival, they realize the possibility that Haiqi is pregnant.
