'Doctor Who' new Christmas special prequel - watch
'Vastra Investigates' stars Neve McIntosh as Madame Vastra, Catrin Stewart as Jenny Flint and Dan Starkey as Sontaran warrior Commander Strax.
In the Steven Moffat-penned short, Silurian investigator Vastra and her partner Jenny tie up the loose ends of a criminal investigation and make a new unsettling discovery.
The first prequel to this year's Who Christmas special was screened last month as part of the BBC's Children in Need broadcast.
Festive episode 'The Snowmen' will air on Christmas Day on BBC One at 5.15pm and at 9/8c on BBC America.
Jenna-Louise Coleman will make her debut as new companion Clara in the hour-long instalment, appearing alongside Matt Smith and guest star Richard E Grant.
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Watch a trailer for the Doctor Who Christmas special below: