The plot begins in Heian era Kyoto. A woodcutter and a priest are sitting beneath the Rashōmon city gate to stay dry in a downpour when a commoner joins them and they begin recounting a very disturbing story about an assault and murder that took place. Neither the woodcutter nor the priest understand how everyone involved could have given radically different accounts of the same event, with all three of the people involved indicating that they, and they alone, committed the murder.

The woodcutter claims he found the body of a murdered samurai while looking for wood in the forest, three days earlier. He first found a woman's hat (which belonged to the samurai's wife), then a samurai cap (which belonged to her husband), then cut rope (which had been used to bind the husband), then an amulet. Finally, he discovered the body, upon which he fled to notify the authorities. The priest claims he saw the samurai traveling with his wife the same day the murder happened. Both men were summoned to testify in court, where a fellow witness presented a captured bandit, who claimed to have followed the couple after coveting the woman when he glimpsed her in the forest.

Tajōmaru, the bandit and a notorious outlaw, claims that he tricked the samurai to step off the mountain trail with him to look at a cache of ancient swords he had discovered. In the grove, he tied the samurai to a tree, then brought the samurai's wife there with the intention of assaulting her. She initially tried to defend herself with a dagger but was overpowered and then seduced by the bandit. The wife, ashamed, begged Tajōmaru to duel her husband to the death, to save her from the guilt and shame of having two men know her dishonor. Tajōmaru honorably set the samurai free and dueled with him. They fought skillfully and fiercely, with Tajōmaru praising the samurai's swordsmanship. In the end, Tajōmaru killed the samurai, causing the wife to flee in terror. At the end of his testimony, he is asked about the expensive dagger used by the samurai's wife. Tajōmaru claims he forgot about it in the confusion after the fight, and laments leaving it behind, as the dagger's pearl inlay made it very valuable.

The wife's testimony tells a different story. She claims that Tajōmaru left immediately after assaulting her. Once he was gone, she begged her husband for forgiveness, but he simply stared at her coldly. She freed him and begged him to kill her so that she would be at peace, but he continued to stare at her with loathing. His contempt distressed her so greatly, she fainted while standing over her husband, with the dagger in her hands. She awoke to find her husband dead, the dagger in his chest. In shock, she wandered through the forest until she came upon a pond. She attempted to drown herself, but failed.

Lastly, the court hears the story from the perspective of the samurai, as told through a medium. The samurai claims that after the assault, Tajōmaru asked the wife to travel with him. She accepted, but asked Tajōmaru to first kill her husband so that she would not feel the guilt of belonging to two men. Shocked, Tajōmaru grabbed her and gave the samurai the choice: let her go or kill her. The wife broke free and fled, with Tajōmaru giving chase. Tajōmaru failed to recapture her, gave up, and returned to set the samurai free. Tajōmaru apologized, and then departed.