Another seemingly random plot thread in The Witch's Familiar might actually have more significance than audiences first realised. Missy told Clara that she had a daughter once and then in The Girl Who Died, we saw a mysterious girl who knew she was different. Could they be the one and same? There was certainly no mention of her mother in the Viking village. It is likely that Missy will be back in the finale, if not before, and maybe working with Davros and the Daleks in some form. Given how The Woman Who Died ended, it is not unreasonable to assume that Ashildr will be back too? What if all these characters converged with the Doctor and Clara with the revelation that the once innocent Viking Girl was actually the daughter of the Doctor's mortal enemy?