1. Regency/Victorian – Snape is a butler for Earl James Potter who has recently passed without a legitimate heir. The Earldom and the estate has been left to 16-year (or 18) old Harry who has spent most of his life at Boarding School not knowing who his parents were since his mother had ‘not’ been married to his father. Can be Magical or not...
2. Snape is Headmaster when a sentient Hogwarts, imbued and tainted by Voldemort’s spirit (or other reason), holds him captive during the summer holidays after everyone else leaves. Harry, an Auror, must attempt to rescue him since he is the only person the castle allows through the walls.
3. Sirius isn’t quite right when Harry goes to live with him. No one believes Harry since Sirius acts fine when other people are around. No one, except Snape.