In addition to The Doctor, Hartnell plays a different character in this one, who also goes on holiday. And then we get a new, annoying companion.
The Doctor and Steven materialise in 16th century Paris, where catholics are hunting down protestants (and scientifically inclined ones, in particular, it seems) like there’s no tomorrow. They immediately split up, as Doc wants to meet with an apothecary named Preslin, and Steve wants to go sightseeing.
Instead, however, Doc goes on holiday and Steve makes friends with Nicholas and Gaston of the Huguenot resistance when he learns from a girl, Anne Chaplet, that the catholics are plotting another protestant massacre, and he decides to help his new friends thwart it. There is also, however, going to be a political assassination, and he’ll need to stop that as well. But he doesn’t know when that’s meant to happen, nor who the target is.
And just to make things extra weird, the massacre and the assassination are planned by, among other people, the Abbot of Amboise, who looks exactly like The Doctor and is in fact played by William Hartnell. Is it The Doctor in disguise? Steven certainly thinks so. Wonder if he’s right, if we’ll ever find out, or if indeed it even matters…