Regulus Black escaped the Cave, believing he is responsible for the destruction of Voldemort's immortality. After the end of the war, and what he thinks is the permanent death of his old master, Regulus is charged with the protection of his brother's godson while visiting him in Azkaban. Now he has only three primary goals: free Sirius from imprisonment, raise the Potter kid properly until his brother is able to take over, and to thwart those that had wronged his family as best he could. OR: Regulus Black is alive, Dumbledore is dumb (but what else is new?), Sirius might or might not eventually get out of Azkaban, Remus is actually somewhat acceptable parent-figure. Oh there's also some random kid called Harry Potter in here?