In *Kingdom Come: Deliverance 2*, side quests like finding Rosa's book can be easily overlooked, leading to missed opportunities if not completed in time. To ensure you don't miss out on this quest, here's a detailed guide on how to unlock and complete "Rosa's Book."
Unlocking the Rosa's Book Side Quest
To initiate the "Rosa's Book" side quest, you must first complete the "Via Argentum" quest and begin "Taking French Leave." During "Taking French Leave," you'll help the Ruthard family deal with Vavak, either through persuasion or force. Once you've resolved the situation, you'll be directed to speak with Rosa. She'll inform you about a secret passage into Maleshov that can be used to rescue Hans. After discussing the passage, Rosa will request that you retrieve a specific book for her while you're in Maleshov. Be sure to ask her about the book and promise to bring it back to her to officially start the "Rosa's Book" side quest.

It's crucial to complete this quest during "Taking French Leave," as leaving Maleshov with Hans without finding the book will cause the quest to fail. This failure also means you'll miss the chance to romance Rosa. Fortunately, the book is conveniently located on your path to Hans' room.
Finding Rosa's Book
Upon entering Maleshov, head to the largest tower where Hans is located at the top. Use the stairs on the side of the building to enter the tower discreetly. Once inside, you'll find another set of stairs and a small kitchen nearby. Hide in the kitchen until the guards upstairs leave the tower.

Sneak up the stairs to find a room with Lady Ofka sitting inside, facing the fireplace. Stealthily approach her from behind and knock her out. Collect the keys from her body, the podium in her room, and the sword from the chest. In this room, you'll find Rosa's book positioned to the right of the fireplace in a window alcove. Pick up the red book to update your quest objective to return it to Rosa.

While in the area, don't forget to grab another sword from the chest in the adjacent room. This will save you time when meeting Hans, as you'll need two weapons for him and his surprise guest. After securing the items, proceed to the top level and unlock the left door to trigger a cutscene.
Following the cutscene, continue with "Taking French Leave." Although Hans opts out of using the passageway, you can still work towards romancing him by choosing the heart dialogue option, provided you made the same choice in Trosky. From there, sneak to the stables on the north side of Maleshov, dealing with guards as necessary. After clearing a path, signal Hans to ensure he reaches the stables safely.
Open the gate to trigger another cutscene, concluding the quest. Once the cutscene ends, return to Kuttenberg City and visit Ruthard Palace to deliver Rosa's book, successfully completing the "Rosa's Book" side quest in *Kingdom Come: Deliverance 2*.