"The True Identity…!!" (その正体…!!, Sono Shōtai…!!) is chapter 381 of the original Naruto manga.
Jiraiya, despite having suffered severe injuries, managed to capture one of the Six Paths of Pain. He tried to figure out why none of the six resembled Nagato, but reaffirmed that one resembled Yahiko and all had the Rinnegan. He considered if Yahiko had taken Nagato's Rinnegan but put this theory to side as all six Pains had the Rinnegan. In addition, Jiraiya remembered a conversation he once had with Nagato. As the Pain in front of him's forehead protector slipped off, Jiraiya saw the scar on his forehead and recognised him as a ninja he had faced in the past. Knowing for a fact that this wasn't Nagato, Jiraiya decided to test a hunch rather than return to Konoha. He asked the Two Great Sage Toads to go home, but they refused at first however, he managed to convince Shima to take the Pain he captured to Konoha for study. Jiraiya and Fukasaku left the barrier and went up to face the remaining Pains. Jiraiya upon observing them all closely confirmed that he had met all of them before. He had managed to figure out the secret of Pain however, he was soon surrounded and his throat was crushed.