The three main Characters in the game are the three heroes that the player controls.
The three heroes, the Knight, the Thief and the Wizard, come under the influence of The Trine, an ancient Artifact of mysterious power. The Trine binds the souls of the three heroes together as one. They are then compelled to undertake a quest, to find a way to be released from the spell placed on them by The Trine.
A more detailed account of the Characters and their quest can be seen in the following:
The three Characters:
The Quest: