While trying to capture Kabuto as part of their mission, Orochimaru shows up and puts a halt to those plans. Naruto loses control of himself and lets the nine tailed beast take over. This power he is emanating is far stronger and way more malevolent then before to the point that it is also killing Naruto slowly the more he uses it. Yamato is able to seal away the power before anyone else gets hurt, thanks to the power of the first Hokage. Lastly Sai's mission all along was to meet up with Orochimaru on Danzo's orders but the full extent of said mission is still a mystery to Naruto, Sakura, and Yamato.