On this page of our guide to Wolfenstein: Youngblood you will find a detailed description of Missing Partner side mission. This task concerns the infiltration of Laboratory X with the aim of finding the missing Fifi Lacroix.
Who's commissioning the mission: Talk to Floor de Cloet in the hideout, in the catacombs.
Mission difficulty level: The game recommends 42 levels of experience for this task. You can achieve this by completing other side missions, locating secrets, etc. You don't have to wait to get promoted to this level, because at least part of the mission can be completed in "stealth mode".
This task is carried out in the Siegturm / Laboratory X location, where you could unlock a fast travel point (metro station) - see separate pages of our guide for more information.
The exploration of Siegturm begins in the city, so you have to get back to the advertising pole and use the secret elevator in the middle. This will allow the sisters to move to Laboratory X.
In the first area you won't find anything yet - you can eliminate enemies in open battles, kill them quietly or completely avoid them. A big facilitation is that the laser barriers are switched off this time and you don't have to look for alternative ways to reach your destination.
The second area of Laboratory X is connected with this mission. You must examine the laboratory room marked on the mini-map where the Audio Log can be found. You don't need to listen to the log, because the mission objective will automatically be updated.
The next goal of the trip are Bio-Labs. They are located in the next large part of the laboratory X separated from the current one by a large yellow gate that has to be lifted. On your way to them, you'll have a lot of fighting or sneaking around.
Fifi's body is in a room on the ground floor. On the table next to them there are Research Documents. Leave Laboratory X and return with the documents to Floor.
Rewards: 14400 XP, 820 silver coins, 1 skill point.