Atrus, the central character of the Myst series, is descendent from a great civilization of artisans known as the D'ni. The D'ni possessed the extraordinary ability to create worlds, known as Ages, by writing a thoroughly descriptive book outlining its features. The D'ni suffered from their own pride, however, and their civilization fell as the books they wrote were destroyed. Atrus' parents and grandmother escaped from K'veer, home of the D'ni, while the tumult was drawing to a close. Atrus' mother died as he was born, leaving his father in agony as he fled from the pain.
The beautiful skyline of Amateria
More than thirty years later, Atrus has been working on trying to rebuild the civilization of his ancestry, and has written a new age for his family and the D'ni survivors to occupy and thrive within. The name of this new age is Releeshahn, and Atrus hopes for it to be a new beginning for himself, and a place for his new baby daughter to grow up and blossom. His hopes are dashed, however, when an unknown enemy suddenly links into his home, steals the book of Releeshahn, sets the library on fire, and disappears, linking into the book of J'nanin. While Atrus and his wife, Catherine, are busy trying to keep the books from burning up, you boldly flip open the linking book and travel to J'nanin to confront this newcomer and recover Releeshahn for Atrus.
J'nanin is another Age that Atrus had created before as a training ground for his two sons, Sirrus and Achenar. It primarily serves as a hub world which links to several other training ages preserved there, Voltaic, Edanna, and Amateria. The antagonist of the story, Saavedro, indicates that he is luring Atrus there to show him the damage that Sirrus and Achenar have caused to his home world, Narayan, and to his life. He hates Atrus, believing that Atrus behaved magnanimously and refused to repair his dying world, and possibly even encouraged his sons to brutalize Narayan.
Saavedro, the antagonist in Myst III: Exile
After Saavedro retreats, the mechanism holding the book of Narayan retracts, placing the Age out of your reach. As a hologram of Saavedro's face tells you once you enter his chamber, you must travel to the three training ages and collect symbols from them. Once collected, the symbols must be scanned by the mechanism to grant access to the Age of Narayan. Saavedro has also recorded messages for Atrus in several places in the Ages to explain his turmoil, and also as a means of coming to grips with it himself. Thus the player assumes his task of pursuing Saavedro in an attempt to rescue Releeshahn, essentially reclaiming Atrus' future from a man that believes he no longer has one of his own.