Twa Corbies
Severus Snape dies in the floor of the Shrieking Shack – or so it seems, at first.
His soul certainly has departed from his previous life, but for some unfathomable reason he doesn’t move to the Great Beyond. Leave it to Destiny to fuck him up even in the afterlife.
He awakes at St. Mungo’s, alive and intact, in 1975.
And while he could just lie there and curse to his hearts content, he knows that wouldn’t help his situation. He died and ended up in the past, and if there is a way to return to his own time, it certainly won’t waltz in to the Magical Maladies department in St Mungo’s and announce itself.
He is a Slytherin, for Merlin’s sake. He knows how to survive. He knows how to plot. He can deal with this. If he plays his cards well, he can even save Lily.
Thank Merlin, he can save Lily.
So he plots. He starts by getting an ID and a wand, then a Potion Master’s license; he finds a small potions shop in Dragon Alley and starts to make connections for the upcoming war.
While brewing another dose of Calming Draught, the best-selling potion of his new founded ship, he actually realises all the implications the year 1975 comes with.
It’s before the Shrieking Shack incident.
Before that day at the Black Lake.
Before he took the Dark Mark.
Before his downward spiral started.
That means there’s someone else besides Lily that can be saved.
Himself.
Or:
A fed-up 38-year-old Snape ends up fostering a younger version of himself while plotting the demise of the Dark Lord.