Attenborough's Phantoms

From the creator of the mods Peaces Like Us, Sweet Half-Life, and Mistake of Pythagoras:
Long after the extinction of humanity, a group of mysterious humanoids called "Phantoms" living in a former research facility find a collapsed young girl. While they are trying to understand how she got there, an unidentified flying object is rapidly approaching their location...
The volumes division is based on the mobile app releases, and the extra chapter was hidden behind a puzzle accessible from the final chapter.