The Chemotion Files is a series of datasets that can be used to get to know the electronic lab notebook Chemotion ELN. This is the second lesson in the series. With these datasets, people can get familiar with some of the features of the electronic lab notebook in a mystery, escape-room-like style "game". How to use The Chemotion Files: Download the .zip file and go to the Chemotion ELN Demo hosted by the KIT (https://demo.chemotion.ibcs.kit.edu/home), this is the official demo version of the electronic lab notebook. If it is your first time there, then you need to sign up. After signing up, you can directly log into the electronic lab notebook and upload the .zip with "import collection". After the import is finished, you will see one new collection in the ELN called "The_Chemotion_Files" with a sub folder called Case_002-The-Missing_Spectra. Now you can start and try to solve the mystery of the Hidden sample. You can check the following video for details on how to "play" The Chemotion Files - Case 002": https://www.youtube.com/watch?v=Soqtw4KTT0I The dataset was tested with the Chemotion ELN version v1.8.1 Comment: The data used in this riddle was published by Simone Gräßle (see cited works). I recommend not to check out the original dataset before solving the riddle; otherwise you might spoil your fun with the riddle.