I’ve been thinking about the title of this episode. Most obviously, it refers to …well…ice. Yet, the ice isn’t thin at all, is it? In fact, it is so sturdy that a several ton elephant can take a stroll without it even cracking.

If we think of “thin ice” as a metaphor for the potential threat or failure of something we depend on, Bill walks on “thin ice” at every turn. The dramatic tension in the episode is caused not only by the situational danger she faces, but by her doubt in the Doctor. Can she trust him was they walk together on their adventures?

That long shot of Bill’s foot as she first steps on the ice visually captures this theme.

Before Bill even leaves the TARDIS, she expresses her fear of standing on the “thin ice” of Regency era racism. Shortly thereafter, she expresses fear about “stepping on a butterfly” and fatally altering her own timeline. Later, Bill’s  trust and belief in the Doctor as a benevolent being almost fails when he chooses not to save a little boy from the ice. Finally, in the most literal example of the theme,  the ice cracks beneath Bill’s feet after the Doctor frees the monster.

In the third episode of a series that seems to be prioritizing Bill’s character development and her relationship with the Doctor, this episode solidifies both priorities by strengthening through challenge. Throughout the episode, we get to watch Bill learn what we, the viewers, learned a long time ago. The Doctor is a mercurial man, making decisions based upon his own idiosyncratic value structure rather than the values of the people or culture of others. The Doctor responds to each one of Bill’s “thin ice” moments, ultimately proving that he is trustworthy enough to go adventuring with.

First, she must trust him that she will be safe in her brown skin as she roams the Thames of 1814 London. When Sutcliff verbally accosts Bill, the Doctor punches him in the face. She must choose to trust that the Doctor is not a killer, even after he fails to save a child. Although the little boy dies, the Doctor finds a way to ensure the safety of the remaining children for the rest of their lives. Finally, when the ice is cracking under her feet, Bill places herself literally and figuratively in the Doctor’s hands as he hauls her off the ice single handedly.

Over and over again, Bill walks on thin ice with the Doctor, having to trust that he is a person of knowledge, wisdom and compassion. In the process, their friendship is tried, tested and strengthened.

So, at a quarter of the way through Series 10 (already?!), what do we know?

The Doctor and Bill have become family to each other. The human tendency towards taking shortcuts can have fatal consequences. And, the Doctor is trustworthy, even when at first glance, his actions seem threatening.

I could see those themes leading to a pretty cool Series finale.

However, at this point I only have one question…when will we get some Missy and Master action going on???????

P.S. A few random thoughts…

Did anyone else wonder if the critter under the Thames was the same poor beast from the Torchwood episode Meat?