You know what this is for.
Come on, Ferrets. Come and play!
Ok. At present, Horace Slughorn is potions master. So this fic is either pre-Snape or post-HBP.

I think post-HBP would be cool, but it's not up to me, it's up to the ferrets who post the next few bits.
This is all in Mrs. Norris' P.O.V. and so while she can't communicate much with people other than Filch (and maybe McGonagall), she should be able to talk to the other animals in the castle.
Because all I've given her is a smell to follow and the House Elves making breakfast, the next few posts get to decide:
- Pre-Snape or Post-HBP?
- If Pre-Snape, is Snape a student (Marauders Era?) or is it before/after him?
- If Post HBP, is Hogwarts running?
- Are there students there or is the school closed for the war/summer/whatever?
- Is Harry at school or is he off looking for Horcruxes?
- Is Voldemort still around or has he been defeated? Harry & the gang?
Loads of other options here, gang. Have fun!