This is amazing! I love the connection between Darkness and obfuscation and how you made it a source for Sherlock to use instead of making it the cause of his genius and deductive abilities. And how there's this tension and temptation shadowing all of their interactions but John fights it off. Perfect characterization. I sure love me a stubborn John. And I love Mycroft's conversation with John about being a good man, because it reminds me of that Terry Pratchett quote about how a good man will shoot you dead instead of making you suffer, so you'd better pray to be at the mercy of an evil one. This whole thing is just brilliant and well-done and I can't wait for reveals so that I can read your other stuff!