A humanoid alien (Aamir Khan) lands on Earth naked on a research mission in Rajasthan but is stranded when the remote control for his spaceship is stolen. He manages to get the thief's cassette recorder. On the same day in Bruges, an Indian Hindu woman Jaggu (Anushka Sharma) meets a Pakistani Muslim Sarfaraz (Sushant Singh Rajput) and falls in love with him. Jaggu's father (Parikshit Sahni) objects to their relationship citing religious differences. He consults godman Tapasvi Maharaj (Saurabh Shukla) who predicts that Sarfaraz will betray Jaggu. Determined to prove them wrong, Jaggu asks Sarfaraz to marry her. At the wedding chapel, she is heartbroken when she receives an unsigned letter, believing it is from Sarfaraz, calling off the marriage due to cultural differences.
Jaggu returns to India and becomes a TV reporter. She meets the alien and is intrigued to see him distribute leaflets about the "missing" God. She earns his trust by rescuing him when he attempts to take money from a temple's collection box as a refund on God's broken promises. The alien tells her that he is a researcher from another planet. His people know nothing about dressing, religion, or verbal communication. They transfer ideas by holding hands. The alien learned to fit in with humans by wearing clothes and using money stolen from "dancing cars".
In a flashback, after being accidentally hit by a truck, the alien is befriended by bandmaster Bhairon Singh (Sanjay Dutt), who takes him along with his troop. Bhairon takes him to a brothel, where the alien holds a prostitute's (Reema Debnath) hand for six hours and thus learns the Bhojpuri language. Bhairon suggests him that his thief may be in Delhi. The alien leaves for Delhi. Due to his strange behavior, people assume he is drunk and call him "peekay" (Hindi for drunk); the alien adopts PK as a name (his people have no language and thus no names).
People tell him that only "God" can help him find his remote. PK sincerely practices Indian religions, including Hinduism, Sikhism, Christianity and Islam, attempting to find "God", to no avail. He later discovers that Tapasvi has his remote, who claims it was a gift from God and refuses to return it. Jaggu promises PK that she will recover his remote and he can go back home.
PK conjectures that Tapasvi and other godmen must be dialing a "wrong number" to communicate with God and are advising the public to engage in meaningless rituals. Jaggu encourages the public to expose fraudulent godmen, by sending their videos to her news channel. This "wrong number" campaign turns into a popular mass movement, to the dismay of Tapasvi. Meanwhile, Bhairon finds the thief and contacts PK, telling him that he sold his remote control to Tapasvi. PK realizes that Tapasvi was a fraud all along and that it was not a "wrong number". Bhairon brings the thief to Delhi, but both die in a terrorist attack. The attack is later declared by Tapasvi's followers to be protecting their Gods.
Tapasvi decides to confront PK on-air. Tapasvi asks PK what the "right number" is. PK says that "God that created us all" is the only concept people should believe in and that the other "duplicate Gods" are artificial. Tapasvi argues, saying that PK is trying to take people away from their Gods and that they will not stand for their Gods being taken away. He claims he has a direct connection to God and refers to his prediction of Sarfaraz's betrayal to try to prove that Muslims are liars. PK, having absorbed Jaggu's memories earlier, realizes that Sarfaraz did not write the letter to Jaggu.
Jaggu contacts the Pakistani Embassy in Belgium where Sarfaraz worked part-time. The embassy tells her that Sarfaraz still loves her, and is now living in Lahore. Jaggu and Sarfaraz reconnect, and Tapasvi is forced to return PK's remote.
Meanwhile, PK has fallen in love with Jaggu but refrains from telling her because she loves Sarfaraz. Having filled multiple audio tapes with her voice alone, he takes two suitcases full of tapes and extra batteries when leaving for home. He lies to Jaggu saying that the suitcases contain a variety of Earthly noises which he will miss, such as crows and car horns. Jaggu realizes his love for her but does not directly confront him about it. PK does not even look back while going. After his departure, Jaggu publishes a book about him, with Sarfaraz and her family assisting. Her father whistles at her reading, implying that after many years he is very proud of Jaggu.
One year later, PK returns to Earth on a new research mission on human nature with several other members of his species (including one played by Ranbir Kapoor) ReadMore>