The story follows a nameless lone drifter known as (Kevin Costner). He is a mutant who has evolved with gills behind his ears and webbed feet, allowing him to breathe underwater. He is cold, cynical, and survives by trading rare supplies and staying away from the politics of the atolls. The Conflict: Smoker Attacks
In a climactic battle, the Mariner infiltrates the Smokers' tanker to rescue Enola. He manages to destroy the ship and the Deacon, eventually decoding the tattoo with Helen's help. They find —a lush, mountainous island (implied to be Mt. Everest). While Helen and Enola stay to rebuild society on land, the Mariner , realizing he belongs to the ocean, sails back out into the open sea.
In a future where the polar ice caps have completely melted, the Earth is entirely covered by water. Humans live on floating "atolls"—massive, rusted metal communities—and survive by scavenging "dirt," which has become the most valuable currency on the planet. The Protagonist: The Mariner
The peace is shattered when a violent gang of pirates called , led by the tyrannical Deacon (Dennis Hopper), begins raiding atolls. They are searching for a young girl named Enola , who has a mysterious map tattooed on her back that supposedly leads to "Dryland"—the last remaining piece of solid earth. The Core Journey