In the Indian city of Chandrapore, Dr Aziz meets Mrs Moore when she enters a mosque at night. He criticises her, thinking that she has not removed her shoes before entering, when in fact she has. They talk about religion and about their families and quickly become friends.

Cyril Fielding, the principal of Government College, invites Aziz over for tea at the suggestion of Mrs Moore. Aziz arrives early, just as Fielding is getting dressed. When Fielding breaks his back collar stud, Aziz offers him his own. He is upset when Fielding refuses this courtesy, seeing it as typical of the problems that beset the English and the Indians in India. Fielding apologises and accepts the stud. They are joined by Dr Godbole, a Brahmin who teaches at the College, and by Mrs Moore and Adela Quested, who has come to Chandrapore to marry the City Magistrate, Mrs Moore's son Ronny. Adela is clearly fascinated by Aziz's stories about the Mogul Emperors, but is also slightly apprehensive when he describes some of their more intimate customs. Adela and Mrs Moore express a desire to see the 'real India' and Aziz suggests an outing to the famous Marabar Caves. Dr Godbole and Fielding take Mrs Moore to see the school grounds. Ronny arrives and is clearly upset at seeing his mother missing and his fiancée having tea with Aziz. Adela gets angry with him and asks that their engagement be postponed. After they leave, Fielding apologises to Aziz for Ronny's rudeness.

Aziz organises a trip to the Marabar Caves but Fielding and Godbole miss the train. Mrs Moore reassures him that all will be well. Adela is clearly enraptured by the journey and by the Indian countryside. Outside the caves, she tells Aziz that she will marry Ronny after all. Aziz tells her of his late wife and of their children and describes their wedding ceremony. Mrs Moore becomes agitated by the echo inside one the caves and comes out weeping. She suggests that Aziz and Adela visit the other caves without her. Fielding and Godbole arrive a little later, just as Adela is seen making a hasty trip down the mountain slope and getting a lift in a passing car.

At the club, Fielding learns that Adela was picked up in a state on great distress and covered in cactus spines. She has accused Aziz of having attempted to rape her in one of the caves. Fielding refuses to believe it, but finds the whole British community against him. He resigns from the club so as to support Aziz. Ronny speaks with his mother. She is clearly distressed, not so much about Adela but by the emptiness she found in the caves. Deeply disturbed by the events, she claims that Adela has been suffering from a 'spiritual illness' for quite some time. She is adamant that she cannot help or give evidence and insists on going back to England.

Aziz is put on trial. He is humiliated when the cherished photo of his wife and his private letters are used in evidence. Mrs Moore is called by Aziz's lawyer, but Ronny reveals that she died on the ship home. When Adela gives her evidence, she suddenly says that she made a mistake and withdraws her accusation. She is abandoned by the other members of the British community and by Ronny. Fielding is the only one to take pity on her. She claims that for a long time the echo of the caves has been ringing in her ears, but that now it has gone. Fielding speculates that she unconsciously decided to destroy her India upon realising that she didn't really love Ronny. He convinces Aziz not to seek compensatory damages against her, as it would ruin her financially at a time when she has nothing left. The two men part, hoping that one day it may be possible for them to be true friends.