Riven, Entrapment

When it opens, Atrus immediately links to Riven to investigate, and meets the Stranger at the brink of the Fissure. Depending on the player's actions, the ending to Riven varies. In the canon ending, the Stranger tricks Gehn into the prison book and releases Catherine. Atrus and Catherine thank the Stranger, before linking back to the Age of Myst. The Stranger then falls into the Star Fissure, to be taken on the path back to his world. Different player actions can result in the Stranger's entrapment in the prison book, or even his death.

Source: Wikipedia > Riven