The year is around 1300 AD and weak magic exists, as in demigods, magical auras, potions and alchemy, but not hardcore wizard magic. The city you live in has become ridden with plague and hundreds die every day. No one is certain, but most believe the vermin that populate the streets were the origin of the disease. The alchemists and doctors have tried everything, but no one can seem to stop its spread. What do you do? How would you cure the city, stop the plague’s spread, or would you simply pack up and hope you can outrun it?
Edit: Oh, think the Rat Plague in Dishonored, maybe I was subconsciously thinking about that when I wrote this.
Hire the Pied Piper to deal with the rat problem. Remember to pay him so he doesn’t also take your children.
Cats. Lots of cats. Magical cats with magical auras. Unleash them upon the rodent infestation!
Stockpile a whole bunch of supplies. Make sure I have a fresh water source that’s going to be untainted. Barricade myself in and wait it out, hoping there’s no inadvertent fire that will purge the city.
Set the entire city on fire and burn the plague out of it! The strong and the rich will survive!
Quarantine the city, preventing anyone from leaving and stopping it from spreading further. And hope I have immunity when the entire thing burns through the city. Not literally burns this time.
Read some fantasy stories that tackle plagues. But also historical stuff. I think the first one I read was Tamora Pierce’s Briar’s Book, which has a plague hit the city. She’d a sickness in the first Alanna book too.
sounds like a good idea . Personally yeah I’d form a kitty army (especially as in this Tony Robinson documentary he said there was a job where people went round killing kitties as they thought they might be spreading the plague in England :’( :’( ) So I’d also expect lots of mass hysteria, so I might just pack up and leave with a cat, maybe taking a couple of logical, level headed people with me who wont be prone to freaking out.
What? Outrun a plague? Nah, that shouldn’t be an option, it’s too boring. I would suggest that you give the protagonist a motive to cure the plague - some important person or thing the protagonist will lose if he doesn’t cure the plague.
Also, it would be best if the player were powerless and yet save the day by finding a cure to the plague.
Make sure that you have a fleshed out story from this idea (I hope you have a lot of ideas) so this doesn’t seem short and is not only restricted to “curing the plague”. Also do remember that a cure to a plague takes months if not years, so do include everything in depth and give the player hardships and obstacles.
Remember, you do not have to give all happy endings, maybe the player can fail due to wrong choices and are unable to cure the plague (please no stat checks for endings, everyone hates it) .
You’ve selected a great idea and have good lore and world-building, please try to keep things realistic and to the ground. Weak magic should mean weak magic, not bringing back the dead or moving boulders. Alchemy should be treated as scientifically as possible : all this will increase the immersion in the game and keep things difficult for the player.
Finally, these are all just my suggestions, you or someone else may not agree with them, and that’s completely fine. The final decision should is up to you, these suggestions are just what I think.
For evil MCs: a blood ritual that requires sacrificing a person who has got the plague, but got cured by luck (to produce a magical vaccine with the antibodies in his blood).
Oh why be just evil! So, your loved one/child/parent/best-friend whatever, comes down with the plague early! You’re distraught! You’re worried about them surviving, and they do eventually manage to pull through. They’re the only person you know, for certain has survived.
And eventually you discover that the magical vaccine requires you to sacrifice someone who’s already survived, in order to save the entire city! Will you do it? Will you look for someone else to sacrifice? Will you decide that you could never engage in such nefarious magics. And what if you do it and then it doesn’t work?
Hmm does a Study in Steampunk have a plague section? I’ve vague memories.
The bubonic plague (which we associate with rats) was actually spread by the fleas (on the rats) I think… so that could be a nice complication for your cat army (since the fleas would simply migrate more effectively via cats).
A lot of steampunk has cholera, caused by contaminated water.
Both wonderfully deadly & fast-moving (wonderfully for fiction, not real life…) with a relatively simple solution.
. Personally yeah I’d form a kitty army 
(especially as in this Tony Robinson documentary he said there was a job where people went round killing kitties as they thought they might be spreading the plague in England :’( :’( ) So I’d also expect lots of mass hysteria, so I might just pack up and leave with a cat, maybe taking a couple of logical, level headed people with me who wont be prone to freaking out.