As November 1984 unfolds, Soviet submarine commander Marko Ramius takes command of the Red October, an advanced Typhoon-class ballistic missile submarine known for its groundbreaking "caterpillar drive," which allows it to evade detection by passive sonar. Departing from northern Russia, Ramius embarks on a mission intended for joint exercises with the Alfa-class attack submarine V.K. Konovalov, led by his former pupil, Captain Tupolev. Under the guise of routine military operations, Ramius discreetly eliminates the political officer Ivan Putin, while misleading his crew with false orders to conduct missile drills off the eastern coast of the United States. Unbeknownst to the Americans, the USS Dallas, a Los Angeles-class attack submarine, simultaneously loses contact with the Red October once its advanced technology comes into play.
On solid ground, CIA analyst and ex-Marine Jack Ryan returns from London, engaging in discussions with Vice Admiral James Greer, the CIA's Deputy Director. After briefing the officials about the situation, the gravity of the threat presented by Red October and its maverick captain casts a dark shadow. Despite growing concern, Ryan's insight leads him to believe that Ramius intends not to attack but to defect to the United States, a hypothesis that must be validated within just three days before the Navy is ordered to destroy the submarine.
As tensions rise, Tupolev is tasked with intercepting and eliminating Red October. On board the USS Dallas, a clandestine saboteur disrupts operations, resulting in a catastrophic failure of the caterpillar drive during a perilous journey through an underwater canyon. Petty Officer Jones, a talented sonar operator, manages to devise a method to detect Red October using his acoustic software, prompting the Dallas to chart a course for interception. Amidst these unfolding events, Ryan boards the Dallas, striving to convince its captain, Commander Bart Mancuso, to make contact with Ramius and uncover his true motives.
As the confrontation between the U.S. and Soviet Union intensifies, a bold order from the Soviet ambassador is issued: capture the rogue Red October. The U.S. governmental response is swift, convinced of Ramius' malicious intent, and orders the Dallas to take decisive action. However, Ryan firmly believes that Ramius intends to defect, persuading Mancuso to reach out to the submarine's commander.
Surprised by the Americans' keen awareness, Ramius accepts Mancuso's offer of aid, orchestrating a staged nuclear reactor "emergency" that necessitates surfacing and evacuating the crew. As a U.S. frigate approaches, Ramius makes a bold decision to submerge again, leaving his crew in life rafts behind. In a daring rescue mission, Ryan, Mancuso, and Jones take to a rescue sub to board Red October, where Ramius unexpectedly surrenders command and seeks asylum for himself and his crew.
Their escape, however, is jeopardized as Konovalov surprises them. The two Soviet submarines engage in a delicate cat-and-mouse chase, while Loginov, a cook revealed to be a GRU agent, resorts to violence on the bridge, severely injuring Ramius' first officer, Vasily Borodin. In a dramatic turn, Ryan confronts Loginov, ultimately killing him after the assailant wounds Ramius.
In an escalating battle, Konovalov launches a torpedo at Red October, but through quick thinking and countermeasures, the Dallas redirects it back towards Konovalov, leading to its destruction.
With Red October's crew now rescued, they witness the explosion from the deck of the U.S. frigate, left in disbelief by what seems to be Ramius’ betrayal as he appears to have scuttled the submarine. Successfully navigating Red October to the bustling waters of the Penobscot River in Maine, Ramius reveals to Ryan his horrific motivation for defection: he feared that Red October was designed for a preemptive nuclear strike against the United States. Appalled by this likelihood, Ramius chose to act against such orders. As Ryan prepares to return home, he finally finds a moment of peace on his flight, seated beside a teddy bear intended for his daughter.
