This section contains spoilers which could ruin the game for you if you have not played it before, or have not yet reached the end.
This may contain spoilers from the other Myst games.
It could be argued that the story of Myst starts with Atrus trapping Gehn on Riven by throwing himself and the Myst book into the Fissure [see: Book of Atrus]. However the events of Myst takes places some 20 years after the events detailed in The Book of Atrus. In that time Atrus and Catherine have gotten married and had two sons, Sirrus and Achenar.
Atrus sought to teach his sons the ways of The Art and to respect the Ages and their inhabitants, however he failed to teach his sons this respect. As a result Sirrus and Achenar trampled through the Ages, plundering them ripping apart the civilizations within before burning the Descriptive Books. Atrus knew that greedy travelers might arrive one day so he wrote to Prison Ages and placed them in his library on Myst Island, in hopes to trap the traveler. He never thought it would be his own sons who would be trapped.
Sirrus and Achenar conspired again their parents. Telling their mother, Catherine, that Atrus had gone to K’veer she Linked there to find him. Not seeing Atrus there she assumed he had returned to Riven after all these years and so Linked to Riven. The sons removed a page from the Linking Book in K’veer that lead back to Myst then tricked Atrus in Linking to K’veer trapping him back in the room his own father had imprisoned him in several decades before. Having trapped both of their parents, Sirrus and Achenar decided to venture into the Ages that Atrus had forbade them from going to, thus trapping themselves. Unknown to Atrus the Myst Linking Book he had dropped into the Fissure years ago had arrived on Earth and into the hands of “The Stranger”. The Stranger Linked to Myst and found the place empty, by following clues left around Myst Island and the few Ages that survived the destruction wrought by Sirrus and Achenar, The Stranger was able to discover the truth and free Atrus.
Disappointed with the betrayal of his sons Atrus burns the Linking Books to the two Prison Ages apparently destroying the Link for good. The events of Myst were the beginning of a long friendship between Atrus and “the stranger” with the latter assisting Atrus in confront Atrus’ father Gehn in Riven
Achenar was the oldest of Atrus and Catherine’s children and bother to Sirrus and Yeesha.
Unlike his brother Sirrus, Achenar’s degree of insanity was more outwardly visible. Evidence of his mind frame could easily be seen from his habitats in the various ages in the form of weapons, torture devices and various other instruments.
Although we do not know how involved Achenar was in the plot to acquire the Red and Blue books of Spire and Haven, evidence of his involvement could be seen in the note left to him by his brother Sirrus in the Channelwood Age.
Achenar used the blue Linking Book where he was trapped in the prison Age of Haven until he was freed by Sirrus some 20 years later [see: Myst IV Revelation].
Atrus is descended from D’ni and Surface dwellers. His grandmother Ti’ana discovered D’ni and married Aitrus a guildsman of D’ni [see: Book of Ti’ana]. Their son, Gehn, went on to marry a surface dweller called Keta after the fall of D’ni. Gehn and Keta had Atrus who is 1/4 D’ni and 3/4 human.
Honest and noble, Atrus was left to grow up in the Cleft with his grandmother Anna (Ti’ana) after his father Gehn fled when his wife died during child birth. At the age of 14 Atrus was taken to D’ni with his father who had returned for him. Atrus however grew very disillusioned with his father and tried to escape back to the Cleft and to his grandmother Anna.
As punishment Atrus was locked in the bottom of K’veer, the island mansion in which Gehn had lived since he arrived in D’ni, with the Riven Descriptive Book. With the assistance of Anna and a Rivenese villager called Katran (Catherine), they managed to trap Gehn on the Age of Riven [see: Book of Atrus]
Atrus settled on the Age of Myst with Catherine, who he later married, and his grandmother Anna. He later had two sons Sirrus and Achenar who later betrayed him and his wife in their desire for riches the Ages in Atrus’ library held. Atrus was trapped back in the same room his father had imprisoned him in due to his sons schemes, he was later freed by a stranger who found the Myst Linking Book that Atrus had dropped into the Fissure [see: Book of Atrus].
Atrus later left Myst island to start rebuilding the D’ni civilization, with the help of other D’ni survivors and the people of Averone they began to rebuild on the Age Releeshahn (The Whole) that Atrus had written for them [see: Book of D’ni]. Atrus and his wife then settled in to their new home they called Tomahna, it was there they had their new daughter, Yeesha.
Sirrus was the youngest of Atrus and Catherine’s two sons and brother to Achenar and Yeesha.
Sirrus was very clever, cunning and resourceful he also had the lust for power and wealth to go with it. Unlike his brother Achenar, Sirrus insanity was kept under-wraps and it is only through his plans for power that you get a glimpse of just how far the man is prepared to go. Living in excessively opulent rooms in various Ages, Sirrus would indulge in his alcohol and drug habits.
It is speculated that Sirrus and Achenar were working with the Black Ship Pirates of the Mechanical Age [see: Mechanical Age Journal], this is due to evidence being discovered in the Stoneship Age (a Black Ship Pirates flag). Just how involved they were with the Black Ship Pirate we do not know at this point.
Sirrus was more than likely to be the mastermind behind the plot to attain the Red and Blue books from Atrus’ library. He along with his brother were trapped in these Prison Ages that Atrus had set up to trap greedy explorers. Sirrus was trapped in the red book of Spire before escaping some 10 years later [see: Myst IV Revelation].