In *Kingdom Come: Deliverance 2*, a crucial side quest, easily missed and unrepeatable, involves retrieving Rosa's book. This guide ensures you don't miss out.
Unlocking Rosa's Book Side Quest
Before Rosa requests your help, complete "Via Argentum" and begin "Taking French Leave." After assisting the Ruthard family with Vavak (through force or diplomacy), speak with Rosa to learn about a secret Maleshov passage for rescuing Hans. She'll mention the book, prompting you to start "Rosa's Book" by asking about it and promising to retrieve it.

This quest is only available during "Taking French Leave." Failing to find the book before leaving with Hans results in a failed quest and prevents a potential romance with Rosa. Fortunately, the book is conveniently located on your way to Hans.
Upon entering Maleshov, locate Hans in the tallest tower. Use the external stairs to enter, then find another stairwell and a nearby kitchen. Hide in the kitchen until the guards above leave the tower.

Sneak upstairs to a room where Lady Ofka sits. Knock her out, take her keys, the keys from the podium, and the sword from the chest. Rosa's book is in this room—a red book in the window alcove to the right of the fireplace. Grab it; your objective updates to returning it to Rosa.

Take the sword from the chest in the adjacent room. This saves time later when equipping Hans and his guest. Proceed to the top floor, unlock the left door, and trigger a cutscene.
Following the cutscene, continue "Taking French Leave." While Hans may initially refuse the passage, a heart-based dialogue option (requiring a previous heart choice in Trosky) can advance a romantic subplot. Sneak to the northern stables, subduing and hiding guards. Signal Hans to ensure his safe arrival at the stables.
After the final cutscene, return to Kuttenberg City and deliver Rosa's book at Ruthard Palace, completing the quest.