In the near future, Earth is under a relentless assault by an invading force of alien creatures known as Mimics. These hive-minded beings have already conquered continental Europe, and humanity’s conventional military units are helpless against them. The United Defense Force (UDF) plans a desperate, large-scale invasion of the French coast, hoping to turn the tide of the war.

Major William Cage is a U.S. Army public relations officer who has never seen a day of combat. When he is ordered by General Brigham to cover the Normandy landing from the front lines, Cage attempts to refuse and is promptly arrested, stripped of his rank, and sent to a forward operating base at Heathrow Airport. There, he is assigned as a private to Master Sergeant Farell’s J-Squad, a unit of misfit soldiers. Thrown into the brutal beach assault, Cage is killed within minutes. In his dying moments, he manages to kill an unusual, large blue Mimic and is drenched in its blood.

Instead of dying, Cage awakens back at Heathrow the previous morning, forced to relive the same day over and over. Each time he dies on the beach, he returns to the same moment. During one of these cycles, he encounters Sergeant Rita Vrataski, a legendary war hero known as the Angel of Verdun. Unlike the others, she believes his story and instructs him to find her in the next loop. When he does, she reveals that she once possessed the same time-resetting ability he now has, having won the Battle of Verdun by reliving it countless times. She lost the power after a blood transfusion.

Rita takes Cage to Dr. Carter, a disgraced scientist who explains the Mimic hierarchy. The creatures are a single superorganism controlled by a central brain called the Omega. The Alpha Mimics act as the Omega’s lieutenants; if an Alpha is killed, the Omega automatically resets the day to prevent its own destruction. Cage inadvertently hijacked this ability when the Alpha’s blood soaked into him. The only way to end the war permanently is to locate and destroy the Omega.

Over hundreds of loops, Cage endures grueling training under Rita, transforming from a terrified coward into a highly skilled warrior. They use his foreknowledge to survive the beach and venture deeper into enemy territory. As they search for the Omega, Cage has visions of its location. However, they soon discover the Mimics are aware of his power and laid a trap with a false vision. Using a prototype tracking device, Cage and Rita determine the Omega is hidden beneath the Louvre Pyramid in Paris.

During their escape from UDF headquarters, Cage is severely wounded and given a blood transfusion, permanently stripping him of his ability to reset time. With only one life left, he convinces Rita and J-Squad to join him on a final, suicide mission to Paris. They fight through the Louvre, where the squad sacrifices themselves so Cage can reach the Omega. As Cage is mortally wounded, he manages to detonate a belt of grenades directly into the Omega’s core, destroying the central intelligence and causing all Mimics on Earth to shut down instantly.

Dying in the explosion, Cage is once again enveloped in the alien blood. He awakens in a helicopter flying over London, two days before the invasion was set to begin. In this new timeline, General Brigham announces that a massive energy pulse in Paris has neutralized the alien threat. Cage arrives at Heathrow, where J-Squad is alive and well, and he is still a Major. He finds Sergeant Rita Vrataski in a training yard. She does not recognize him, but as she greets him coldly, Cage simply smiles, knowing the nightmare is finally over.