- Madame Lavoisier: What am I to do? Where can my husband be?
- Arno: Madame Lavoisier? What's the matter?
- Madame Lavoisier: My husband and I were about to conduct an experiment on a poisonous gas, but he went for a walk and hasn't returned! I'm worried about those hooligans who follow Marat! Who knows what they might have done. They're often found near the Panthéon.
- Arno: Don't worry. I'll find him.
Arno made his way to the Panthéon and managed to locate Marat's thug. Tracking him, Arno found a building near the Bièvre where Lavoisier was being kept.
- Thug 1: Look, old man, scribbles on paper don't tell us much. How does it work?
- Lavoisier: Hardly "scribbles", dear fellow; each line details a step in the process. It's quite fascinating, actually, if one-
- Thug 1: Shut it! Philippe's got the paper, he'll figure it out. If not, well, maybe your wife can help us.
- Lavoisier: What?
Arno killed the thugs and spoke to Lavoisier.
- Lavoisier: They took my formula, we can't let them use it! It's an improvement on the smoke bombs I developed for you Assassins to make them poisonous. Some fellow here has it.
- Arno: I'll find it. You go reassure your wife.
Arno located a building nearby and entered it, finding two thugs examining one of Lavoisier's bombs.
- Thug 2: We've got to find somebody who can und-
The two thugs accidentally detonated the bomb, causing the building to catch fire. After escaping the house, Arno saw more of Marat's thugs and killed them as well, finding the formula on one of their bodies. Arno then returned to Lavoisier's residence.
- Madame Lavoisier: Arno! We're so glad to see you!
- Lavoisier: My good fellow! And the formula is safe?
- Madame Lavoisier: We knew you'd put things right.
Arno rescued Lavoisier and managed to recover his formula.