“I told you, you don’t steer the TARDIS, you reason with it.”
“Unsuccessfully, most of the time.”
A companion’s first visit to history, time to reiterate the rules about stepping on butterflies, and decide whether we’re dressing to blend in or not. (We are.) So there’s a moment that echoes The Unquiet Dead as Bill takes a first careful step onto snowy ground in the 19th century. And some more as she deals with how the Doctor might solve the threat.
There are, however, more echoes of The Beast Below, including the human choice of what to do about the suffering creature being used for human gain. I like this particular solution, especially the knock-on effect. (And the Torchwood episode Meat too.)
And how a companion deals with the deaths that follow. Bill’s reaction is very real, and given time and focus.