Ray Breslin, portrayed by Sylvester Stallone, is a former prosecutor who co-founds Breslin-Clark, a specialized security firm located in Los Angeles, dedicated to evaluating the security measures of maximum-security prisons. His mission is to infiltrate various penitentiaries, examining their layouts and the behavior of the guards to identify vulnerabilities, which he exploits to facilitate his own escape while preventing criminals from slipping through the cracks of the justice system.
His life takes a significant turn when he and his business partner, Lester Clark, receive an enticing multi-million-dollar offer from a CIA agent named [Jessica Miller](Jessica Miller) to evaluate a secret prison designed to contain terrorists, hidden in remote areas across the globe. This facility, funded and built by the CIA, remains unacknowledged by the US government. Compelled by a promise of double his usual fee, Breslin surprisingly agrees to the assignment, disguising himself as a Spanish terrorist named "Anthony Portos" in New Orleans. However, complications arise when his captors remove the tracking device from his arm and administer drugs during transport, causing him to lose his ability to prove his true identity.
Upon awakening, Breslin finds himself in a complex of glass cells with no visual connection to the outside world. Here, he meets fellow inmate Emil Rottmayer, and together they stage a performance to analyze the solitary confinement cell's use of blinding halogen lights meant to disorient and dehydrate the inmates. They also encounter the prison's physician, Dr. Kyrie, who shows a surprising amount of empathy for their plight, offering medical assistance after their repeated infractions.
As Breslin explores the prison's layout, he notices that the floor consists of aluminum, yet the rivets are made of steel. He devises a plan for Rottmayer to obtain a metal plate from Warden Willard Hobbes's (Jim Caviezel) office prior to being thrown back into solitary confinement along with Javed, a fellow inmate. Unbeknownst to Breslin, Hobbes pursues the notorious Victor Mannheim, whom he believes to be Rottmayer’s superior. In solitary, Breslin shares his true identity with Rottmayer and reveals he's been betrayed, expressing his intentions to escape and uncover the traitor.
Utilizing the procured metal plate, Breslin discovers he can reflect light onto the rivets to heat and eventually pop open a floor panel leading to an underground passageway. He sneaks through this passage and uncovers that the prison is situated inside a cargo ship amidst the ocean, heightening the challenge of an escape.
Breslin and Rottmayer meticulously observe the guards' daily routines while Breslin feeds Hobbes false information regarding Rottmayer's connections. Clark and Hobbes keep in contact, with Clark insisting that Breslin remain locked up. Meanwhile, colleagues Abigail Ross and Hush grow wary of Clark's agenda following the sudden freeze on Breslin's paycheck. Their investigation into hacked documents reveals that the prison, dubbed "The Tomb," is tied to a for-profit organization linked with a private security agency; Clark is being lured into betrayal with a lucrative salary.
Concurrently, Hobbes makes it clear that he recognizes Breslin's true identity, and alongside Chief Security Officer Drake, he intends to ensure Breslin remains incarcerated for life. Rottmayer cunningly persuades Hobbes to allow him on deck for his nightly prayers under the pretenses of using a makeshift sextant to pinpoint the ship's coordinates. By combining this information with weather observations, Breslin calculates that they are in the Atlantic Ocean nearby Morocco.
Breslin approaches the infirmary, convincing Dr. Kyrie to assist him and Rottmayer by transmitting a disguised email to Mannheim. Breslin fabricates a message signaling an impending riot, tricking Hobbes into concentrating security in cell block C. This distraction facilitates Javed's instigation of a real riot in cell block A, granting Breslin and Rottmayer a critical opportunity to escape towards the deck while alerts echo throughout the facility.
In a fierce confrontation, Breslin takes down Drake, but tragically, Javed loses his life in the crossfire. As Breslin navigates to the engine room to reboot the power systems, Rottmayer hatches a plan to access the deck while a helicopter sent by Mannheim engages in a dramatic gunfight with the guards. Although they manage to board the helicopter, Breslin is caught in a torrent of water that forces him downwards. In a daring move, he eliminates Hobbes by igniting an explosion near a cluster of oil barrels, paving the way for their escape.
They ultimately land on a beach in Morocco, where Rottmayer reveals his true identity as Mannheim, with Miller being his daughter. The earlier disguise of "Portos" had been a signal indicating Breslin's allegiance. Back at a Moroccan airfield, Ross informs Breslin that Clark has gone missing, but Hush has traced him to Miami, securing a plan to confront him aboard a shipping container.
