Somehow you end up in the Immaterium, before the Chaos Gods. Dont ask how you got here.

Khorne: WHO GOES THERE. It says angrily, sitting on his skull throne Nurgle: A mortal? Perfect, time to put my new plagues to good use... It says, coughing and wheezing every few words Tzeentch: How... interesting. It says, sounding largely uninterested despite being interested Slaanesh: I can give you pleasure beyond your mind's wildest desires... Take your pick...~ It says, wasting no time in trying to get you on their side