A British Special Boat Service (SBS) was formed during World War II by the British Navy, gaining a reputation for effectively neutralizing hidden enemy positions and often collaborating with MI6. This elite force laid the groundwork for the modern U.S. Navy Seals.
The story centers on John Stratton, portrayed by Dominic Cooper, an SBS soldier working within the Intelligence Detachment in Northern Ireland. Alongside him are mission specialists Aggy, played by Gemma Chan, Spinks, portrayed by Jake Fairbrother, and Cummings, in the role of Tom Felton. Together, they embark on a perilous mission to infiltrate an Iranian bio-chemical weapons factory. However, upon arrival, John and his partner, Marty, played by Tyler Hoechlin, discover a horrifying scene: all the factory workers have been killed, and the vault containing the bio-chemical weapons is alarmingly empty. They realize they have arrived too late, and their position is compromised. Just as they attempt to escape, John's partner is tragically shot in the neck, leading to his untimely death.
In the aftermath, John finds solace living on a boat in Ireland, where the only person he can truly call a friend is Ross, portrayed by Derek Jacobi. His life takes a turn when Sumner, played by Connie Nielsen, his MI6 boss, urgently summons him. She reveals that a significant quantity of weapons of mass destruction stolen from the facility is still unaccounted for, and she needs John's expertise to track down the terrorists responsible for the theft. To aid him in this task, Hank, portrayed by Austin Stowell, is assigned as John's new partner.
As John dives deeper into the investigation, he analyzes video footage of their failed rescue with Aggy to identify the mastermind behind the attack. Sumner identifies the main assailant as Grigory Barovsky, played by Thomas Kretschmann, a former FSB agent who was presumed dead for two decades. Sumner shares a troubling piece of history: two decades ago, Barovsky was a rising star in the FSB. MI6 had labeled him a double agent, which led to a FSB operation to eliminate him. However, this was based on a false premise, as Barovsky is very much alive and poses a significant threat.
The former agent harnesses the deadly bio-chemical weapons, unleashing them on an unsuspecting community in Ukraine, resulting in the fatalities of 150 individuals. His weapon is alarmingly efficient when deployed aerially, capable of causing mass destruction from an altitude of 1,000 feet. A critical figure in this unfolding nightmare is Tariq Alawi, whose expertise in bomb-making is invaluable for transforming the raw bio-chemistry into deployable weapons.
In a daring operation, the team captures Alawi, who reveals that the bio-chem has been activated and ominously named "Satan's Snow." Under pressure, Alawi provides information leading them to an Italian engineer named Greco, who has engineered a prototype drone for Satan's Snow, further complicating the scenario. When Barovsky appears to collect the drone, he uncovers the surveillance set up by John and Hank, mistakenly believing Greco is betraying him. In a fit of rage, he kills Greco and attempts to escape with the drone, only for Hank to defy orders and engage Barovsky. They manage to seize the drone, but Barovsky slips through their grasp.
Realizing the urgency of the situation, John theorizes that Barovsky has three other drones ready for his command. During his discussions with Sumner, he mentions Sergei, who was Barovsky's superior when he was betrayed. In a remarkable uncovering of past events, John suggests that perhaps Sergei never intended to kill Barovsky but instead used him strategically to undermine Britain's operations in Iran, which would have catastrophic international repercussions.
As the story unfolds, it is revealed that while seeking revenge, Barovsky has stolen crucial files containing information about foreign agents, including Cummings. With this knowledge, Barovsky threatens Cummings to retrieve the fourth drone or risk exposure as a Russian agent to Sumner. The tension escalates as Sumner fears Barovsky may target Moscow with the deadly Satan's Snow, leading Cummings to propose an exchange of intelligence with the FSB for a hostage in Russia.
As the team investigates, they discover that Cummings is the infiltrator among them, leading to a whirlwind of revelations and confrontations. In a twist of fate, Cummings goes missing. With the clock ticking, Spinks manages to decipher the guidance system of the fourth drone, soon realizing that the true target is London, not Moscow.
As Sumner tracks Barovsky's entry into London, John is tasked with stopping him. In a heart-stopping chase, they recover two drones, but Barovsky still manages to escape with the last one. In a shocking turn, Cummings abducts Aggy and, in a moment of desperation, takes his own life. This dramatic climax leads to Barovsky entering the warehouse to load the last drone onto a London bus, cleverly concealed by Aggy.
With determination, Aggy assists John and Hank in locating the bus in downtown London. They heroically intercept the vehicle, resulting in a thrilling confrontation with Barovsky, who is ultimately neutralized before he can unleash his deadly weapon.
In the aftermath of these harrowing events, John takes a moment to ask Aggy out on a date, hinting at the possibility of a new beginning amidst the chaos they have all endured.
