Need Hans's help in *Kingdom Come: Deliverance 2*'s "For Whom the Bell Tolls" quest? You'll need to brew a Fever Tonic, a crucial step in reaching Trosky Castle. Here's how:
Fever Tonic Recipe and Location in *Kingdom Come: Deliverance 2*

The Fever Tonic recipe resides within the Surgeon's Workshop in Trosky Castle. Access is granted in two ways: sneak in, or convince the chamberlain. To persuade him, offer to create a digestive potion for his stomach ailment. Successful skill checks will unlock the workshop.
Alternatively, after delivering the horseshoe in "For Whom the Bell Tolls," speak with Cook Fanka at the forge. Offer assistance with her locked chest; she'll lead you to the noble's kitchen. The ailing chamberlain is there. Convince him you can help to gain access. Crafting a digestive potion alongside the Fever Tonic further solidifies your access and allows a meeting with Thomas.

If persuasion fails, steal some food, exit the kitchen, and use the courtyard stairs leading to another kitchen door (guarded). Bribe the guard with the stolen food. Sneak upstairs to the Surgeon's Workshop; the journal containing the recipe is on the bookshelf.
Brewing the Fever Tonic

The necessary herbs are already at the surgeon's station. Follow these steps:
- Pour wine into the cauldron.
- Add 3 handfuls of Feverfew.
- Lower the cauldron and boil for 2 turns of the sandglass.
- Grind a handful of Elderberry Leaves.
- Add the ground Elderberry Leaves.
- Add 2 handfuls of Ginger.
- Take a phial from the bottom left shelf.
- Distill the tonic using the Still.
Don't worry about failures; ample herbs are available. Once brewed, deliver the Fever Tonic (and the digestive potion, if made) to the chamberlain to meet Thomas, or use the noble's kitchen to find Thomas and Adele in the chapel to complete the quest.