The Inquisition didn’t exist in the middle ages, at least not as some sort of omnipresent heresy-hunting institution. There was an inquisition set up against the Cathars in 12the century Languedoc, but it was limited in duration and focus. And there’s never been an inquisition in England, which is where this thread is talking about.
There also wasn’t really much danger you’d be called a witch. The big witchcraft fears and witch hunts didn’t start until the Rennaisance.
Frank Herbert made a similar prediction - in the Dune appendix notes on the Orange Catholic Bible and the Council for Ecumenical Translation, there’s a poem called Brown Repose.
Better study medieval herbalism. I think that the understanding and use of medicinal herbs was more advanced than people here realize. You might also want to check out Ellis Peters Brother Cadfael mystery series. The protag is a former soldier turned monk, working in the monastery herb gardens. Ellis Peters was known for her historical research, so if you can discover some of her sources, that may help.
If your protag is a modern-day herbalist – and there are a fair number – or a pharmacologist or chemist who grows medicinal and culinary herbs (and there is quite a bit of overlap) as a hobby – s/he might come up with some interesting concoctions. Getting hold of anything not locally grown would have been costly, however.
Yeah, some of you are being pretty harsh on the high middle ages (NOT the dark ages, thank you very much). Fitting in in general would be the trickiest bit (especially to play the part of a learned physician), but unless you actively make some enemies in the church, or actively spread herterodox theology, there’s no one lying in wait to spring upon your differences.
The real religious intolerance in Europe didn’t come until later.
People most likely knew that their water was unhealthy, and that’s why they drank ale or wine. Probably one of the reasons why bathing was so limited, in addition to all the reasons cited in other threads (what hard work it was to heat water, make soap, etc.). So persuading people to wash their hands with boiled water or distilled alcohol would not be so hard. Getting servants away from their other duties to boil sufficient quantities of water (and keeping the previously boiled water clean), and distilling sufficient alcohol to use for cleansing purposes might be more problematic. If you have enough servants, you could do it.
If you’re interested in the Black Death, surely you meant the mid-14th century, not the 13th?
Maybe the best thing (for a lasting effect) would be to teach the scientific method, to give people the tools to understand, test and verify some of the facts you’d be layin’ on 'em, like circulation of blood, disease pathogens, what the internal organs actually do, etc. It wouldn’t be hard to make a simple microscope (or a compound microscope if you know how).
I don’t know what to do about Prince Edward’s dropsy, though.
Yeah, I was thinkimg “1300’s” and it came out as “13th Century.” My bad. I’ve been reading Philip Ziegler’s The Black Death (widely regarded as the definitive book on the subject) and become very interested in the period. I know better than to mix up the “hundreds” with centuries. I don’t how I let that slip by.