Harry Potter and the Half Blood Prince.... OMG... still processing.
Could R.A.B. be Regulus Black? Would that be why he was killed on Voldemort's orders? And if so, is the actual Horcrux locket in the House of Black somewhere? Does Kreacher have it? And will Harry truly not return to school?
GAH... I'm gonna have to read it again to sort all this out in my head.