RPGs and related matters, by Craig Oxbrow.
Alien robots who are spreading the plague of 1665. The Plague Doctor costume is just a way to hide themselves amongst the general population.Maybe they're spreading the plague to make it ready for whatever species hired them to make the earth fit for colonisation.Just a plot idea; it's probably terrible.
That totally works. So much so that Doctor Who pretty much did it in my formative years. :)
See I've now just got a image of Kai wandering round Plague infested London, while Effie looks at him despairingly...