In the southern Pacific, there exists a tiny island that cannot be found on any map: Cocoa Island, a beautiful little paradise that rests atop a coral reef. It is said that the legendary Chaos Emeralds rest here, and so did the hero of our story, once upon a time before he met his speedy blue idol. The following events take place prior to Tails' first encounter with Sonic:
During a sunny afternoon on Cocoa Island, Miles "Tails" Prower is taking a nap just outside his research lab, Tails House. His slumber is interrupted by a huge explosion, and before Tails can say "stop, drop, and roll" the whole place is ablaze. A frantic Flicky reports the bad news to a confused Tails: the imperial Battle Kukku Army has invaded Cocoa Island. The dictator Great Battle Kukku 15th has discovered the Chaos Emeralds on the island, and intends to use them to conquer the entire world. Tails is the only one who can put a stop to the imperial army.
Source: Wikipedia, "Tails Adventure", available under the CC-BY-SA License.