Riven's story continues where Myst and its companion novel, The Book of Atrus, left off. Atrus knows the ancient art of creating "linking books", specially written books that serve as portals to other worlds known as "Ages". Atrus needs the player's help to free his wife, Catherine, who is held hostage in her home Age of Riven, which is slowly collapsing. Her captor is Gehn, Atrus' manipulative father and self-declared ruler of Riven. Thirty years earlier, Atrus and Catherine trapped Gehn on Riven by removing all of the linking books that led out of the Age. The final book they escaped from Riven with, leading to the Age of Myst, fell into the Star Fissure, a rift leading out of the damaged Age of Riven into a mysterious, space-like void. The linking book was not destroyed but was instead found by the player, leading to the events of Myst. Catherine was later tricked into returning to Riven by her sons, Sirrus and Achenar, whereupon she was taken hostage by Gehn.