The scheming Lannister family are not the only ones who should be watching their backs from Maisie Williams.

The 17-year-old actress, who plays Arya Stark on “Game of Thrones,” began filming a guest starring role on the BBC’s time-traveling sci-fi drama “Doctor Who” today. “I'm so excited to be working on 'Doctor Who' as it’s such a big and important part of British culture,” she said in a statement from the network. 

“Who” executive producer Steven Moffat would only say that Williams’ character “is going to challenge the Doctor in very unexpected ways. This time he might just be out of his depth, and we know Maisie is going to give him exactly the right sort of hell.”

The show, currently starring Peter Capaldi (“The Thick of It”) as The Doctor and Jenna Coleman as his companion, is in the midst of filming two period pieces, ominously titled “The Girl Who Died” and “The Woman Who Lived.”