The Utapauans were invaded by forces of the Confederacy of Independent Systems (CIS). The Separatist council was gathering there, but General Grievous decided to move them to Mustafar because of an impending Republic attack. Obi-Wan Kenobi got to Utapau and had a "secret" meeting with the Tion Medon, who was the leader of Pau City. He went off to find Grevious and kill him, which he thought would end the war. Obi-Wan found Grevious, and there was a lot of gesturing and showmanship, but finally they started fighting. Many Battle Droids, Super Battle Droids, and Destroyer Droids had circled around the two. Apparently, they had learned how to dispose of a powerful enemy by watching old episodes of Batman. Rather than just overwhelm and gun down the Jedi, they watched. It was then that the Clones showed up and attacked.At this point, Grevious tried employ a move which he had perfected over the course of the Clone Wars. This move was called "getting the hell out of there". He did this on his wheel bike, a strange device that Hasbro got backwards. Anyway, Obi-Wan was able to keep up with Grievous by riding alongside him on a varactyl, some crazy screetching dino-bird thing. The two fought each other like madmen, until finally they both dismounted near Greivous's ship. The two continued to tussle, until Obi-Wan shot Grievous in his gut sack, which was apparently was flammable.
Anyway, The battle raged, and the Clones kicked ass. Eventually, they seized the entire planet. With Greivious dead, it seemed the Republic would be victorious. However, Order 66 came down, and the clones fired on Kenobi. He escaped in Grievous's ship. The War was indeed winding to a close.