The Witcher 2 Story
Beginning of the Game
At the beginning of the game, Geralt is in the dungeon for the crime of assassinating Foltes, the king of Temeria. The story of the game begins with Geralt telling Vernon Roche about the events in this dungeon. The narration starts from any part of the story according to the player's choice. After completing the stories at the beginning of the game, Roche helps Geralt escape from the dungeon. The journey begins when Geralt escapes from the dungeon and reaches the ship Roche is waiting for.
Flotsam
The second part of the story takes place in the town of Flotsam, where rebel elves and dwarves live. In this town, there is a rebel group that helps Letho, who killed Foltes, the king of Temeria. Geralt begins to gather information by walking around the town and completing the necessary quests. After making some progress, the player learns that Letho collaborated with two witchers and killed King Demavend as well. Geralt finds Letho's hiding place and goes to catch him. Letho defeats Geralt but does not kill him. It is how Letho pays his debt, as Geralt saved Letho's life in the past. Letho goes to the inn in town where Triss is and forces Triss to cast a teleport spell. Letho's goal is to kill Henselt, the King of Kaedwen.
Aen Seidhe
The next part of the story takes place in Aen Seidhe. However, players have two choices for the structure of the story before this point. Depending on the player's choice, the story will continue with Roche or rebel elves. Since the author's choice in this article is Roche, the rest of the article will be based on this story.
When Geralt and Roche reach Aen Seidhe, they encounter a curse. This curse causes dead warriors to resurrect and fight as ghosts. At this point in the story, Geralt must lift the curse to enlist King Henselt's help. Geralt begins to obtain the objects he needs to lift the curse by talking to the king's archmage.
Two witchers next to Letho want to assassinate King Henselt. However, Geralt notices them and prevents the assassination. It leads to a concrete clue for Geralt. Geralt learns from the injured and dying witcher that they are taking orders from the lodge of sorceresses.
End of Story
Geralt finds Letho's hiding place and defeats him. At this point, Geralt learns that Nilfgaard is forcing the witchers to assassinate him. Geralt remembers everything, completely regaining his memory. During the Rivia massacre, Yennefer risked dying to resurrect Geralt.
However, Ciri saved both their lives and took them to another world. In this world, Wild Hunt found the two of them and kidnapped Yennefer. Geralt found them and offered himself in exchange for Yennefer's freedom. Geralt escaped the Wild Hunt and was dragged ashore with amnesia.
At this point in the story, you can either kill Letho or let him go. To me, Letho is considered innocent because he was forced by others. Whichever you choose, at the end of the story, Geralt will set out in search of Yennefer.