The sequel to Sonic Chaos.
Dr. Robotnik has managed to capture all of the Chaos Emeralds. Unfortunately for him, an accident in the testing phase of his new ultimate weapon, the Atomic Destroyer, scatters the Emeralds back across the island. While Sonic and Tails are out to retrieve them, they are cut short by Knuckles the Echidna. Robotnik has already reclaimed the yellow Emerald, and he's duped the island guardian into believing Sonic and Tails are out to steal the Emeralds.
Meanwhile, a sneaky treasure hunter named Nack the Weasel (Fang the Sniper in the Japanese version) is taking advantage of the commotion to take the Emeralds. He does not know of the true power of the Emeralds, but he does know the large, pretty gems would fetch a high price on the market, so he sets out to take them for himself before the others do. Now it's a mad four-sided race for the Chaos Emeralds.
The choice is given of playing as either Sonic or Tails. Sonic has the ability to do the Strike Dash/Super Peel Out as he does in Sonic Chaos that gives him a speed burst and temporary invincibility. Tails has the ability of flight in this game.
Source: Wikipedia, "Sonic Triple Trouble", available under the CC-BY-SA License.