In Kathmandu, Nepal, a band of rogue sorcerers led by Kaecilius infiltrates Kamar-Taj, the hidden sanctuary of the Masters of the Mystic Arts. After murdering the librarian, they steal pages from a forbidden text belonging to Kaecilius’s former mentor, the Ancient One. As they flee through a portal to London, the Ancient One traps them within the Mirror Dimension, a hidden reality unseen by ordinary people. She defeats several of the intruders, but Kaecilius and his remaining followers escape with the stolen ritual.

In New York City, Dr. Stephen Strange is celebrated as one of the world’s finest neurosurgeons. Brilliant but deeply arrogant, he values prestige, wealth, and intellectual superiority above all else. While driving to deliver a lecture, Strange becomes distracted and crashes his car at high speed. Though he survives, the nerves in his hands are catastrophically damaged. Multiple surgeries leave metal pins implanted in his fingers, but his hands remain uncontrollably unsteady, ending the surgical career that defined his identity. His former partner and colleague Christine Palmer tries to support him, but Strange becomes bitter and obsessed with finding a cure.

After exhausting his fortune on failed treatments and experimental procedures, Strange hears of Jonathan Pangborn, a former paraplegic who somehow regained the ability to walk. Strange tracks him down and learns that Pangborn was healed through mystical means. Pangborn directs him to Kamar-Taj, where Strange is reluctantly admitted and introduced to Karl Mordo. There he meets the Ancient One, who initially dismisses him but changes her mind after sensing his potential. She demonstrates the existence of magic by thrusting Strange’s astral form from his body and exposing him to the vast multiverse, forcing him to accept realities beyond science.

Strange begins training under the Ancient One and Mordo, learning the manipulation of energy, portals, and dimensional forces. He studies in the library now overseen by the stern master Wong. Strange learns that Earth is protected from interdimensional threats by three Sanctums located in New York, London, and Hong Kong. Together they form a shield around the planet. While Pangborn chose to use magic only to restore his body, Strange is warned that true mastery demands sacrifice and service.

A naturally gifted student, Strange advances rapidly through months of study. His hunger for knowledge drives him to secretly read forbidden texts, where he discovers the Eye of Agamotto, an ancient relic capable of manipulating time. Wong and Mordo warn him that tampering with time can unleash catastrophic consequences. They also reveal that Kaecilius turned against the Ancient One after losing faith in mortality and becoming obsessed with eternal life.

Using the stolen ritual, Kaecilius begins summoning Dormammu, ruler of the Dark Dimension, a realm where time does not exist. To weaken Earth’s defenses, Kaecilius attacks the Sanctums, first destroying the London Sanctum. The disruption transports Strange to the New York Sanctum, where he is forced into battle. Though inexperienced, he uses his intelligence and the aid of the sentient Cloak of Levitation to hold off Kaecilius until Mordo and the Ancient One arrive.

During the confrontation, Kaecilius reveals a devastating truth: the Ancient One has secretly prolonged her life by drawing power from the Dark Dimension herself. Strange and Mordo are shaken by the revelation. Kaecilius then mortally wounds the Ancient One before fleeing to Hong Kong. Strange rushes her to the hospital, where Christine Palmer desperately tries to save her while Strange battles attackers in astral form. Accepting her death, the Ancient One shares one final conversation with Strange, telling him that strict rules alone are not enough and that he must learn when to break them for the greater good.

Strange and Mordo travel to Hong Kong, only to find Wong dead, the Sanctum destroyed, and the Dark Dimension already consuming Earth. Defying Mordo’s warnings, Strange uses the Eye of Agamotto to reverse time, restoring the city, reviving Wong, and undoing the destruction. As Kaecilius’s followers are dragged into the expanding darkness, Strange enters the Dark Dimension alone to confront Dormammu directly.

Knowing he cannot defeat Dormammu through force, Strange traps both of them inside an endless time loop. Each time Dormammu kills him, the moment resets and begins again. After enduring countless repetitions and realizing he cannot escape, Dormammu agrees to withdraw from Earth if Strange ends the loop. Strange accepts on the condition that Kaecilius and his followers are taken away with him. They receive the immortality they sought, but are transformed into tortured servants trapped forever within the Dark Dimension.

In the aftermath, Mordo becomes disgusted by both Strange and the Ancient One for repeatedly violating natural law. Believing the world suffers because there are too many sorcerers abusing power, he abandons Kamar-Taj. Strange returns the Eye of Agamotto, which Wong reveals to be one of the Infinity Stones, and takes up residence in the New York Sanctum as its new guardian, continuing his studies with a humbler sense of purpose.

Months later, Thor arrives at the Sanctum seeking help locating Odin while keeping Loki under watch. Strange agrees to assist them, provided they leave Earth once their mission is complete. Elsewhere, Mordo confronts Pangborn and strips him of the mystical energy that allows him to walk, declaring that he intends to correct the imbalance caused by reckless sorcery.