As the advanced nuclear submarine Seaview embarks on its trials within the frigid Arctic waters, Captain Lee Crane and his dedicated crew remain blissfully unaware of the impending chaos that looms above. Their mission, directed by the brilliant scientist Admiral Harriman Nelson, is to maintain radio silence for a solid 96 hours in the depths of icy isolation. Yet, their efforts are soon interrupted as the polar ice cap begins a catastrophic fracture, releasing massive boulders into the sea. When they finally resurface, an astonishing scene greets them: the sky is ablaze with a fierce inferno.
After rescuing scientist [Miguel Alvarez](himself) and his loyal canine friend from Ice Floe Delta, the Seaview receives a frantic distress call from Mission Director Inspector Bergan at the Bureau of Marine Exploration. The alarming message reveals that a meteor shower has set off apocalyptic fires, triggering a chain reaction that drastically raises global temperatures.
In light of this escalating crisis, the President (unnamed) urgently convenes with Admiral Nelson for a critical meeting with the United Nations Scientific Committee. Together with Commodore Lucius Emery, they propose an audacious plan: to launch a nuclear missile from the Mariana Islands to neutralize the fiery belt threatening Earth’s atmosphere. This high-stakes operation, which they believe could "amputate" the inferno from orbit, is something only the Seaview can accomplish. However, chief scientist and delegate [Emilio Zucco](himself) stands firmly against this solution, convinced that the flames will eventually extinguish themselves. He shares his viewpoint with Nelson, who disputes his claims, highlighting inaccurate predictions regarding the burn-out point.
Though their proposal is initially rejected, Nelson and Emery persist, seeking direct orders from the President as time ticks away. Racing against the clock, Seaview hastens to reach the optimal launch position above the Mariana Trench, where angles and trajectories could be life-or-death decisions. During their attempts to contact the President via the Rio-to-London telephone cable, they find themselves entangled in a fierce confrontation with a gigantic squid, thanks to Alvarez's unexpected involvement. Unfortunately, they can only access the London cable, discovering that contact with the U.S. has been severed for 35 hours.
Amid these challenges, a failed assassination attempt on Nelson exposes the presence of a saboteur onboard the Seaview, with suspicions falling first on Alvarez, a fervent believer in divine intervention. Additionally, Dr. Susan Hiller, who discreetly aligns with Zucco's stance, becomes a potential suspect as well.
As the submarine's main generator succumbs to sabotage by a deranged crew member, Captain Nelson faces a daunting choice: to continue with crucial repairs or risk further jeopardizing their mission without radar and sonar support. The Seaview must traverse a perilous minefield, leftover remnants from World War II, where mere inches separate them from disaster. Frustration mounts among the crew, threatening to spark a mutiny. In a decisive moment, Captain Crane and the Admiral grant the discontented crew the option to abandon ship, allowing them to take a lifeboat and chart their own path, should they choose to do so.
As tensions simmer, doubts intrude into Captain Crane’s thoughts regarding the Admiral's strategies and intentions. The situation amplifies when a hostile submarine gives chase into the Mariana Trench, only to meet its doom from the immense pressures of the depths, imploding before it can strike the Seaview.
Meanwhile, the saboteur has successfully cut off the submarine's power. Facing Dr. Hiller atop the shark tank, an explosive confrontation arises as she flees from the secure nuclear reactor core. With her radiation badge now a deadly indicator of her condition, her motives for sabotage become clear: to thwart the Seaview’s objective. Following a violent explosion, Dr. Hiller is sent crashing into the shark tank, facing a grim fate.
Upon reaching the Mariana Islands, the Seaview discovers escalating temperatures that challenge Zucco's prior assertions and endorse Admiral Nelson's planned measures. As Alvarez spirals deeper into madness, convinced of his divine obligation to obliterate Earth, he threatens the team with a bomb. In the face of this imminent threat, Captain Crane acts decisively, ordering the launch of a nuclear missile from outside the submarine before Alvarez can intervene, directing it towards the hazardous Van Allen Belt. The ensuing explosion successfully disperses the flames, averting disaster and safeguarding humanity.
As normalcy returns to the sky, the Seaview plots a course homeward, her mission accomplished amidst unprecedented turmoil and uncertainty.
