NOTE: This spoiler was submitted by Joshua
At the beginning of the film, Kaecillius (Mads Mikkelsen) and some other followers break into a temple and steal a book. A voice warns him of performing a certain ritual and then a guy in a yellow robe confronts them. They run away from the temple, revealing them to be in London, and after a fight involving manipulating the world around them, Kaecillius's group escapes.
Meanwhile, Doctor Stephen Strange (Benedict Cumberbatch) finishes up an operation and receives news from Christine Palmer (Rachel MacAdams) about a braindead man with a bullet in his head. Despite fellow doctor Nicodemus West's (Michael Stuhlbarg) objections, Strange operates on the man and safely takes the bullet out, leading the man to gain a full recovery.
After the successful operation, Strange invites Palmer to watch him at a convention, but she refuses. It is clear that Strange is a very self-absorbed perfectionist. While on the way to the convention, Strange, while speeding in his sports car up a mountain, is distracted by new patient records coming in and crashes his car off a hill and wakes up to his hands being nearly inoperable. Despite his best efforts and Palmer's support, he ends up failing with all his experimental treatments, losing nearly all of his money and Palmer.
During physical therapy, a colleague then tells Strange about a certain patient named Jonathan Pangborn (Benjamin Bratt), a man who was fully paralyzed but made a successful and miraculous recovery. Strange seeks out Pangborn and is directed to "Kamar-Taj" in Kathmandu, Nepal.
In Nepal, Strange is followed by the same mysterious man in the opening scene who saves him from being robbed and beaten up by thieves. He then tells Strange where to go and leads him to Kamar-Taj, where he meets The Ancient One (Tilda Swinton). After asking about Pangborn, the Ancient One says that he "re-oriented his spirit" and cured himself. In a rage, Strange tries to confront the Ancient One, but she force pushes his spirit into multiple dimensions to Strange's fear and surprise before bringing him back in and kicking him out. While out, a desperate Strange tries to enter the place to no success.
While this is happening, the Ancient One and Karl Mordo (Chiwetel Ejiofor) discuss training Strange. The Ancient One is weary because of what happened to Kaecillius who went to the dark side (and Strange exhibiting almost the same level of arrogance), but Mordo persuades her to allow Strange in. Strange is then let in and we realize that the watch that was almost stolen from him was a memento of Palmer, engraved with "Time will tell you how much I love you, Christine," revealing that he and Palmer were ex-lovers.
Strange then ventures into a library with Wong (Benedict Wong), and checks out certain books on sorcery. He then notices a section which Wong says is exclusive to the Ancient One and is not to be touched. He says that certain pages were stolen by the former master Kaecillius and threatens Strange over touching the books in that section.
Strange begins his training and struggles in contrast to his fellow trainees. When he complains about his hands failing him, the Ancient One brings out a master with only one hand who manages to conjure a spell. The Ancient One then tells Strange to silence his ego for his power to rise, and teleports him to the peak of Mount Everest, giving him thirteen minutes to conjure a spell to bring himself back or die. Despite the worries of Mordo, Strange manages to pull it off and return.
Later, Strange decides to read up on astral projection but is denied access by Wong. Using the teleportation skills, he learned earlier. However, Strange steals the books and learns how to astral project and have his spirit leave his body. The next day, the Ancient One confronts Strange about the stolen books and instead, teaches him how to conjure a "safe space", which is essentially a backwards reflection of the real world where one can practice all they want without harming the real world and is a shield for threats (the same spell in the opening scene). The Ancient One then warns Strange about Kaecilius and Mordo practices Strange's combat skills, citing that there is a certain relic of power that goes to sorcerers when they are ready.
Later, Strange, after trying to write an email to Palmer, decides to go to the Library. With Wong absent, Strange tries to follow a time manipulating spell in a banned book while wearing the Eye of Agamotto and manages to restore the missing pages of the book as well as an eaten apple. Wong then catches him and scolds Strange over the danger of making repeated time loops and emphasizing that natural laws of the world should not be tampered with. Wong says that as the Avengers save the world from physical threats, they as sorcerers defend mystical threats.
Strange is then brought to a room by Wong and Mordo with three sanctums, one leads to Hong Kong, another leads to London, and another leads to New York. Strange is informed that all three sanctums must be protected by the sorcerers. An overwhelmed Strange decides to leave, but enemies arrive and blast Strange and Mordo into the London sanctum.
In the London sanctum, Strange sees Kaecilius arrive and presumably kill Mordo. Strange decides to fight them, and despite some struggles, he defends himself by sending one of Kaecilius's followers into a desert and closing the passageway and another into a jungle area. Kaecilius then attacks him, but a coat suddenly attaches to Strange and protects him from Kaecilius, and leads Strange to a suit of armor which he traps Kaecilius in. Kaecilius then says that his ultimate goal is eternal life and that the true enemy is time - he was going to summon Dormammu from the Dark Dimension and use power from that. He says Dormammu is not the enemy but the savior of worlds. While Strange is listening, one of the followers suddenly throws a spear into his back and Strange is stabbed. After trying to escape, Strange creates a portal and teleports to New York where he is reunited with Palmer. He convinces Palmer to perform surgery on him and then astral projects to a surprised Palmer.
Meanwhile, the follower of Kaecilius astral projects himself enters the portal to New York (which Strange forgot to close), and the two spirits fight. Strange's physical body flatlines but quickly realizes that defibrillator shocks give him more power. After two powerful shocks, he defeats the follower and is back in his physical body well and good. After telling a surprised and confused Palmer about his journey, he decides to go back to the London Sanctum and finds the physical body of the follower there as well, dead.
Suddenly, an alive Mordo and the Ancient One arrive. They realize that the coat attaching itself to Strange was his relic and the Ancient One promotes Strange to a master, telling him to protect the New York and Hong Kong sanctums before Kaecilius gets to it. Strange is bothered and wants to go, but the Ancient One angrily tells him that he has a delusional ego. Strange, meanwhile, retaliates and questions the Ancient One about her power of immortality, saying that she fed off power from the Dark Dimension.
While this is happening, Kaecilius and his follower's attack, and Strange creates the reversed mirror spell to protect himself, before realizing that they can still die while inside. Strange and Mordo are attacked and chased, and Strange is almost killed but the Ancient One saves them. The Ancient One then fights with Kaecilius after a discussion on his plot, and Kaecilius throws the Ancient One through a conjured portal falling into London vertically from a great height. Despite Strange and Mordo's attempt to save her, the Ancient One falls flat onto the ground leaving her in critical condition.
Strange brings her through a portal to New York where Palmer has her operated on and he astral projects to talk with her spirit. The Ancient One says that she using the power from the Dark Dimension was true, but she only did it to prevent horrible futures, which sadly only got worse after saving a bad one. She then says that Stranger has no future, but only possibilities, due to his arrogance and fear of failing. The Ancient One then tells Strange that the power to heal himself has always been within, and then tells him to stop Dormammu before deciding to die finally. After the Ancient One's death, Strange talks to Palmer and kisses her goodbye.
At the Hong Kong sanctum, Wong prepares the sorcerers for defense. Unfortunately, Kaecilius is already there, and Wong confronts him. Meanwhile, Strange goes to Mordo back in Kathmandu, and despite Mordo's grievances over the Ancient One, he convinces Mordo to go with him to protect the Hong Kong sanctum.
However, when the two arrive, they see that the sanctum has already been destroyed and the dark dimension is fully summoned. Strange then uses the time reversing spell he learned earlier and reverses all the damage, including saving Wong. Kaecilius and company, however, attacks them, and Strange instead decides to fly to the Dark Dimension himself.
In the Dark Dimension, Strange sees Dormammu and attempts to bargain with him. There, Dormammu kills Strange, before Strange appears yet again, having created an infinite time loop to torture Dormammu until he lets him make a deal. Eventually, Dormammu cracks and takes Strange up on his offer - leave Earth alone and set it free.
Back in Hong Kong, everything is back to normal, before Kaecilius and his followers begin disintegrating - part of the bargain was to give them "eternal life" with Dormammu in the Dark Dimension forever. While the world is safe, Mordo is pissed off at Strange violating the world's natural laws and storms off, warning him about the eventual price he has to pay.
Strange and Wong then return to Kathmandu, where Strange returns the Eye of Agamotto (revealed to be an infinity stone). Wong tells him to be ready, and Strange arrives at the New York sanctum and checks his watch - fully embracing his new role as a sorcerer.
Post-Credits Scene #1: Doctor Strange has a visitor over for 'tea,' who is then revealed to be Thor (Chris Hemsworth). Thor has brought Loki with him to New York to search for his father Odin, and Strange offers his assistance.
Post-Credits Scene #2: Mordo visits Jonathan Pangdor (the man who was revealed to be healed of his paralysis via sorcery at the beginning of the film) and confronts him over "abusing his power," saying that sorcerers only abuse nature. He then says that power is given for a reason before stealing Pangdor's powers, rendering him a paralytic yet again. Mordo then says that there are simply too many sorcerers and walks off, implying that he is going to start going after sorcerers around the world.