In the dramatic backdrop of the Korean War in 1952, an American platoon finds themselves captured by Soviet forces and subsequently taken to Manchuria, located in Communist China. Once the conflict concludes, these soldiers return to the United States, and Staff Sergeant Raymond Shaw, played by Laurence Harvey, is heralded as a hero, credited for saving the lives of his comrades in battle. Following a commendation from their platoon's commander, Captain Bennett Marco, portrayed by Frank Sinatra, Shaw is awarded the prestigious Medal of Honor for his alleged heroic deeds. When asked about Shaw, Marco and the other soldiers instinctively proclaim, > "Raymond Shaw is the kindest, bravest, warmest, most wonderful human being I've ever known in my life." Yet, lurking beneath the surface is a profound sense of unease—Marco concedes, "It isn't as if Raymond is hard to like. He's impossible to like!"
Having advanced to the rank of Major, Marco grapples with the torment of recurring nightmares that haunt him. These vivid dreams feature a hypnotized Shaw, who gruesomely murders fellow soldiers under the chilling gaze of prominent military officials from communist countries. The nightmarish scenarios stem from a sinister brainwashing experiment, where Shaw and his platoon are conditioned to believe their captors in the Korean military are harmless, aging American ladies from a local garden club. Driven by a desire to uncover the truth, Marco seeks assistance but is met with resistance from Army Intelligence due to a lack of tangible evidence. However, he soon discovers that another soldier from his unit, Allen Melvin (played by James Edwards), shares his haunting visions. When both Marco and Melvin identify key figures from their dreams as influential leaders in communist regimes, Army Intelligence reluctantly agrees to support their investigation.
Behind the scenes, Shaw's formidable mother, Mrs. Eleanor Iselin (played by Angela Lansbury), wields significant influence, driving the ambitions of her husband, Shaw's step-father, Senator John Yerkes Iselin (James Gregory). Iselin is a flamboyant demagogue reminiscent of Joseph McCarthy, often dismissed by many as a political buffoon. Shaw harbors deep loathing for both his parents, especially his overbearing mother. Senator Iselin's political fortunes rise dramatically when he disrupts a televised press conference to accuse the Secretary of Defense of harboring communists within the Defense Department, eliciting outrage and chaos among the media and government officials alike.
Unbeknownst to all, including Shaw, the Iselins (or primarily Mrs. Iselin) are covert agents for a Stalinist agenda aimed at an ambitious takeover, potentially even reaching the White House. Shaw himself has been conditioned to become an unwitting assassin, his actions activated by the sight of a Queen of Diamonds playing card. Once this stimulus is presented, he must follow through with the orders of whoever triggers him. Shockingly, it is revealed that Shaw's esteemed recognition for valor is a fabricated memory implanted by their communist captors, and the true valiant actions attributed to him never occurred.
Amidst this treacherous landscape, Shaw experiences a fleeting moment of happiness reviving an old romance with Jocelyn Jordan (Leslie Parrish), the daughter of Senator Thomas Jordan (John McGiver), who stands as one of his stepfather’s political adversaries. Their initial relationship was strategized by Shaw as a means to rebel against his parents, yet genuine feelings blossom between them. Mrs. Iselin, however, disrupts their union to further her political ambitions but eventually orchestrates their reunion in pursuit of Senator Jordan's support for Iselin’s unexpected bid for vice presidency.
During a costume party at the Iselin residence, Jocelyn, donning a Queen of Diamonds ensemble, unwittingly activates Shaw's conditioning, leading to their clandestine elopement. Although Senator Jordan tolerates this match, he forewarns Mrs. Iselin of his intent to seek impeachment against her husband should he pursue the vice-presidential seat. In a cruel twist of fate, Shaw’s mother triggers his conditioning, setting him on a path to assassinate Jordan. In a tragic turn, Jocelyn stumbles upon their confrontation and falls victim as a witness to the act. Raymond, shrouded in confusion and grief, is devastated when he uncovers the truth behind the heinous acts he has committed.
As Marco delves deeper into the mystery, he uncovers the pivotal role of the Queen of Diamonds card in Shaw's trance-like state for carrying out murderous assignments. In a desperate attempt to save Shaw, Marco meets with him, utilizing a deck filled solely with Queen of Diamonds cards, effectively revealing the complete narrative of his conditioning. He urges Shaw to sever his ties with the card forever and defy any future commands from those controlling him. Meanwhile, Mrs. Iselin continues her sinister plot, priming her son to assassinate the presidential candidate during a convention speech, thereby securing her husband's rise in the political hierarchy. She chillingly insists that her son may never grasp the full scope of their plot, while she vows revenge against those she believes have manipulated her son's fate.
As the convention unfolds, Marco rushes to halt Shaw’s assignment. Disguised as a Catholic priest, Raymond takes aim, poised to execute his sinister directive. In a shocking climax, instead of carrying out his instructions, he turns the rifle on his stepfather and mother, eliminating them as they lay dead before him. Overcome with despair, he then takes his own life in front of Marco, clad in the undeserved honor of the Medal of Honor, leaving a grim conclusion to a devastating tale of manipulation and tragedy.
