C'est La Vie, Iterum (джен)

Harry Potter is offered the chance to do things again, in a world only slightly different from his own, where all his family are alive and well. Of course he takes the leap.
Except, things aren't adding up - and Harry makes things even more complicated for himself by pretending to be Severus Snape's long-lost son.
 
(or, my own take on C'est La Vie by cywcross, borrowing the premise for the alternate world, but altered and otherwise original.)