Deep beneath the Pacific, the crew of the underwater research station Mana One, funded by billionaire Jack Morris, discovers a hidden ecosystem within the Mariana Trench, previously cut off by a cold thermocline layer. As they penetrate the boundary, their explorations inadvertently disturb the territory of an enormous, thought-to-be-extinct shark species known as the megalodon. During their encounter, they find themselves under attack, leaving their submersible disabled and a crew member trapped at the bottom of the ocean. With the situation dire and time running out, the team is forced to call on Jonas Taylor, a rescue diver whose expertise is unmatched, but whose past experience with the same beast has left him traumatized and skeptical of returning to the depths.

Against his better judgment but driven by a sense of duty to save the stranded explorers, Taylor joins the mission. Upon arrival at the trench, he prepares for one of the riskiest operations of his life. As Taylor and the research team work to execute their plan, the prehistoric predator proves to be a formidable force, threatening not only the lives of the crew but also the wider population above the surface. The rescue mission quickly escalates into a fight for survival, with Jonas leading the charge against the seemingly unstoppable ancient creature.