Vastra Investigates: A Christmas Prequel was a webcast and prequel produced for the 2012 Christmas special. It was the second prequel to The Snowmen to be produced, after The Great Detective, which aired in November during Children in Need.

Madame Vastra, accompanied by her loyal companions Jenny Flint and Strax, is called upon to investigate a Victorian murder mystery. But where is the Doctor?

Another case has been cracked by Madame Vastra; Strax keeps the criminal secure while a Scotland Yard officer, Inspector Gregson, thanks Vastra for her help, commenting how odd Strax looks. Vastra explains the Sontaran's origins, and hers as well when he asks if the skin condition hurts, mistakenly believing her to be human. She perplexes him further by saying she fell in love with her assistant Jenny Flint. Departing in a carriage, both are saddened that the Doctor appears unwilling to leave his TARDIS. However, they then both notice something very odd: it is snowing, yet there are no clouds in the sky...

在1892年的平安夜，大量的雪花提取了人们的意识，并以一个淹死的女家教作为模板，使雪拥有和人类一样的特性，入侵地球，被恐怖威胁的地球需要博士。

而一个年轻家教，克拉拉（S7E01中的天才女孩），当她向博士求助时。博士却在哀悼艾米和罗利，深居简出，坚决不干涉宇宙的问题。

作为老朋友，维多利亚侦探小队。将放纵博士真的放弃人类，或改变他，让他拯救世界，将地球从这个冰冷神秘的而具威胁性的魔爪救出吗？

【超凡智慧间接出现】