Jamal Malik, a young man from the slums of Mumbai, is on the hot seat of the Indian version of the popular game show Who Wants to be a Millionaire. And if that weren't exciting enough, he's one teensy question away from winning the grand prize of 20 million rupees—roughly $436,000 U.S. dollars at the time.
Yeah. That's a chunk of change for anyone… but it's especially life changing from a dude who grew up in some of the most infamous slums in the whole dang world.
But after he's taken into custody by the police under the accusation of cheating, Jamal recounts his life story, explaining how he came to know the answer to each question he faced.
We learn that Jamal and his older brother Salim were orphaned at an early age, and had to scrape by however they could to survive in the slums. Along the way they meet Latika, a young girl who joins their trio—the third musketeer to Jamal and Salim. Soon they're captured by the gangster Maman, who forces them to beg and sing for money. Jamal and Salim are eventually able to escape, but Latika is left behind.
After spending a few years on the road with Salim, Jamal decides to try to find Latika. With his brother's help he's successful, and the three escape together when Salim kills Maman. (Le gasp!) The reunion is short lived, however, after Salim threatens Jamal and steals Latika away.
Time passes, and we find Jamal working as an assistant in a telemarketing office. He decides once more to attempt to find Latika, and starts by successfully contacting his mean bro Salim. After meeting with his brother for the first time in years, he's able to deduce that slumlord Javed Khan, Salim's employer, is holding Latika.
Jamal's able to follow Salim to Javed's compound (which he infiltrates) and finds Latika inside while the game show Who Wants to Be a Millionaire plays on TV. Seeing the ruthlessness of Javed, Jamal tells Latika that he'll wait for her every day at the train station. Fearing for Jamal's safety (as well as her own, obvs) she asks him to leave.
Later, much to Jamal's surprise, Latika is there waiting for him at the train station. However Salim—who seriously is a contender for Worst Brother Ever at this point— arrives with some of Javed's goons to prevent her from escaping with Jamal.
Finally, we catch up to the present timeline, where Our Hero explains to the police that he went on the game show because he thought Latika might be watching. After this reveal, he's released and returned to the show for the final question. What nice cops, huh?
For the final question, Jamal is asked to name the third musketeer from Alexandre Dumas' classic story, The Three Musketeers. Though young Jamal and Salim used to refer to themselves as Athos and Porthos, the first two musketeers, they never learned the name of the third—Latika's role in their trio.
(And this, kids, is why everyone should study great literature.)
Jamal reveals that he does not know the answer, but he decides to play anyway because he has that can-do spirit.
Using his final "phone-a-friend" lifeline, he calls the only number he knows: his brother's. However he's shocked to discover that it's not Salim on the other line, but Latika. Having seen Jamal on TV, she managed to escape from Javed's safe house with Salim's help. Aww, Salim's being nice again.
Like Jamal, Latika doesn't know the answer, but she says that she's safe. A confident Jamal is able to guess the correct answer—Aramis—winning the grand prize. Meanwhile Salim, back in the safe house, sacrifices himself in order to stop Javed from coming after Latika and Jamal.
After his victory, Jamal goes to the train station to wait for Latika. Sure enough, she shows, and the two finally a share a moment of peace together. The movie ends with Jamal and Latika leading an elaborate Bollywood dance sequence to the tune of Oscar-winning song "Jai Ho," as the credits roll.