Doctor Who: Long Live Maisie Williams!

Seriously, we've never identified with a put-upon companion more, waiting for The Doctor (or in our world, executive producer Steven Moffat) to finally make a breakthrough and reveal the big plan already.

[...] warrior aliens known as the confusingly named Mayans (is there a different spelling?) harvest the best Viking fighters in order to literally ingest their adrenaline and testosterone (which glows neon green) to increase their warlike powers and other quasi-scientific-superstitious stuff.

Upset, Viking lass Ashildr (Williams) throws down the gauntlet with the Mayans, which forces the Doctor to conceive of a crazy way to save the remaining villagers that involves electric eels and a psychic storyteller helmet that Ashildr must wear.

When Ashildr dies from exhaustion, the Doctor is sad but then rallies and brings her back to life -- eternal life -- using Mayan technology.

The Doctor, with all of his regenerations, has been painted as a tragic figure, partially because he is destined to be lonely, surrounded by people who keep dying.

With Ashildr joining the ranks of immortals, this adds another intriguing person to the mix who can not only identify with the Doctor's psychological messiness, but also potentially come back in any time period or costume.

First we see unbridled, youthful joy, which transmutes into sadness when she realizes the full impact of losing loved ones, and then eventually becomes an almost wicked look as she bitterly accepts her situation.

First of all, this would keep the door open to more Williams visits.