Reign

The name of the episode was "Chill in the Air." It might as well have been "Night of a Thousand Mistresses." ( more with spoilers )

So what do you think the thing in the cave is?
a) Francis' evil twin brother.
b) Rob Ford in one of his drunken stupors.
c) The Master of Buffy fame stuck in yet another underground church.
d) A Neanderthaler as in The Thirteen Warrior/Eaters of the Dead.
e) Queen Catherine's "mistress."
f) Queen Mary's future husband, Lord Darnley.
g) A Playstation.
h) An evil brain from outer space.
i) A misunderstood polecat.
j) Liberace
k) An Elvis impersonator.