The Mystery of Tobi

is episode 139 of the Naruto: Shippuden anime.

Synopsis
The Leaf ninja continue to fight Tobi, but all of their attacks manage to phase right through him. Zetsu arrives to inform Tobi of the outcome of the Uchiha match, and Madara drops his goofy persona in order to leave the fight and collect the brother's bodies. Sasuke wakes up in a cave and Madara approaches him, introducing himself. An Amaterasu is unleashed from Sasuke's eye, but Madara evades it and mentions how in-depth Itachi's plans were. Sasuke asks what he means, and Madara tells him that Itachi was trying to protect him.