Geillis Duncan

Geillis and Claire are arrested and charged with witchcraft. Claire realizes Geillis poisoned Arthur so she could be free to marry Dougal whose child she is carrying. Claire realizes the Jacobite cause is what brought the two together. Geillis says, “I only regret I have but one life to lose for my country,” which Claire recognizes as Nathan Hale’s famous last words from the American Revolution.

In the courtroom, the two are declared witches. Geillis tells Claire she thinks it is possible (meaning return to the future) and then 1-9-6-8. Geillis announces she’s a witch and Claire is innocent. She confesses to killing Arthur and then pulls down her dress to reveal a “mark of the devil” which Claire realizes is a vaccination scar and realizes Geillis is from 1968.

Geillis is also a time traveler!

Source: The Devil’s Mark