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