The Invisible Hand showed up at Coruscant to kick off the Battle there with a massive Separatist fleet. Grievous was successful in "kidnapping" Chancellor Palpatine on the orders of Darth Sidious (who, unknown to Grievous, was the same guy but with different clothes on).
Pablo Jill was able to get onto the Invisible Hand in a rescue attempt, but was killed by Grievous. Obi-Wan Kenobi and Anakin Skywalker were also able to board the ship through some clumsy comic timing, and killed Count Dooku while rescuing the Chancellor. They met up with Grievous, (who naturally fled like a little girl), and then crashed his big ship on the planet with the help of some overzealous Clonetroopers.