I'm not sure how one can't, that's the first time anybody has told me that. The advertisements and media releases have been pretty straight forwards.
It's lovecraftian horror about two brothers and their betrayal, an ancient civilization being discovered in Egypt, Necromancy, Occult, and other sinister and mature themes. To explain the actual story A to Z would spoil it. But if you know what Lovecraftian horror is, it's pretty easy to guess what you're going to be getting into. If you don't, play the demo!
Triptych is a playable story though so don't expect combat or action. More like an adventure game.