本集讲述博士和泰勒回到当代的伦敦渡过圣诞节。然而，外星人希克拉库斯（Sycorax）却在这时入侵地球。最终，因重生过后昏倒的博士及时醒来，击退入侵者。在英国，这集有980万人收看，并取得正面的评价。
这是扮演第十任博士的大卫·田纳特首次出演整部《神秘博士》剧集。此前，他在《背水一战》的最后一幕出场。同时，这是《神秘博士》首部的圣诞特辑。自此以后，BBC One每年均会制作一部圣诞版的《神秘博士》剧集。

special episode of Doctor Who

Peter Capaldi’s final episode of Doctor Who this Christmas will feature Pearl Mackie as Bill Potts and be called Twice Upon a Time, it was revealed this evening (23 July) during a cast panel at San Diego Comic Con. Viewers will have to wait until Christmas to discover exactly how Bill, who will appear throughout the episode, makes her return.

The series introduces Pearl Mackie as Bill Potts, and also features Matt Lucas as Nardole. Michelle Gomez and John Simm return as their respective incarnations of the Master. The main story arc for the first half of the series revolves around the Doctor and Nardole occupying themselves at a university while they guard an underground vault containing Missy. Missy later travels with the team in the TARDIS, and eventually partners with her previous incarnation as they battle a Cyberman onslaught.

Join the Doctor, as he teams up with an investigative journalist, and a superhero to save New York from a deadly alien threat.