How would sudden immortality change a person?

The Doctor finds out when he is reunited with Ashildr (Maisie Williams), the Viking girl who has lived for more than 800 years thanks to the Doctor giving her a computer chip that repairs her body.

She has had a very interesting life: been a queen, a solider, a witness to tragedy, a healer who’s drowned as a witch, and a highwayman. It’s also hardened her towards we humans who have brief lives. She compares them to smoke, being blown away in an instant. Yet she is also sad, as the Doctor finds out when some of her journal pages have tears on them. She’s even forgotten her original name and just calls herself “me”. She is whatever she wants to be at the moment, because her original self died long after her body should have. It makes sense that she called herself “The Nightmare” in 1651 England, because her immortality is just that to her.

Williams does a wonderful job in creating a character who would enjoy living many lives over the centuries if she just wasn’t so lonely. The Doctor knows something about that. Although he’s had dozens of companions over more than 50 of our years (he’s over 2,000 years old), the toughest part is still seeing them go.

Ashildr begs The Doctor to let her join him in the TARDIS but he already has a companion. So she has another idea, geting his help in taking a rare gem called the Eyes of Hades. It’s rare because it’s alien and she needs it to escape her plight of an endless boring life.  She hopes the amulet can take her away with the help of an alien lion named Leandro (Ariyon Bakare). All they need is to take someone’s life.

They target a robber named Sam Swift (Rufus Hound) who’s about to hung. It’s a pity since he seems to be the Louis C.K. of his day when he’s close to the noose. Ashildr uses the amulet on him, which opens a portal to another world. Leandro’s happy because really he wants his people to invade Earth. Suddenly, Ashildr regrets what she’s done, and admits she really does care. She saves Sam with the other immortality chip she never used and Leandro is literally toasted.

Does this mean Sam will live through the centuries with Ashildr? It’s not clear, thought the experience has given her new purpose. She admits she is quite aware of the impact the Doctor has had on Earth all and thinks maybe she should keep an eye on him. It makes sense, because he made her this way.  He mentions the other person he made immortal, Jack Harkness, and thinks it’s likely she’ll meet him someday. That would be excellent fan fiction, of course. If and when Game of Thrones ends, maybe Williams and the BBC can turn Ashildr into a spinoff.

Clara has taken the week off, but she does provide us with something that hints Ashildr is still around today. Now Clara and the Doctor look ahead to what’s next, while telling her she isn’t going anywhere. The last shot of the Doctor shows that he knows one day Clara will be hopping off the TARDIS for good, just like the others, while he’s looking forward to who is next.

This two-part story with Ashildr was different from previous two-parters because it was more like one story, followed by a sequel. It was a good story about the Doctor deciding to break the rules and creating something that may have been worth his decision. Ashildr was a tidal wave that swept him away too.

Next week, the Zygons are back, and so is Osgood. But how?