There's something very sparse and stark about this, yet there's some really fantastic imagery here. I particularly like "memories scrabbling in the back of Sirius's head, lost to him consciously but squabbling like puppies behind his eyes".
Also, I like the fact that it's Regulus who was the one doing the coercing here. Nice switch.
Sirius' life is so bleak; he's gone full-circle, from a young man leaving the "corrupting influence" of his family home, to a middle-aged man who never had the opportunity to truly grow up, thrust back into that same house and unable to leave it again. The way fragments of his memories come back to superimpose themselves over the present is fantastically dark. Lovely, gritty examination of Sirius' mind.