Sonic Underground Plot Summary: Back on Sonic's home planet, Eggman has collected all 7 of the Chaos Emeralds, and is about to have absolute power when Sonic interferes, causing an explosion that sends everyone from their world to Earth. Sonic and his friends team up with 12 year old Christopher Thorndyke to collect all the Chaos Emeralds and defeat the evil Dr. Eggman. On a mission to save his friend, Sonic accidentaly sets off a machine that performs Chaos Control, warping him, his friends, and Eggman, to a world of humans. Sonic and Co. find a boy named Chris Thorndyke, who they befriend as they take on Dr. Eggman to collect the 7 Chaos Emeralds, stop the water-creature Chaos, and save the world from the Ultimate Lifeform.