The Mystery of Tobi (トビの謎, Tobi no Nazo) is episode 139 of the Naruto: Shippūden anime.
The Konoha ninja continue to fight Tobi, but all of their attacks simply pass right through him. Zetsu arrives to inform Tobi of the outcome of the Uchiha match, and Tobi drops his goofy persona in order to leave the fight and collect the brothers' bodies. Sasuke wakes up in a cave and Tobi approaches him, introducing himself. An Amaterasu is unleashed from Sasuke's eye, but Tobi evades it and mentions how in-depth Itachi's plans were. Sasuke asks what he means, and he tells him that Itachi was trying to protect him.