The intriguing picture shows Sherlock and John in Victorian garb.
The special (not yet confirmed as a Christmas special) is set to air in 2015.
In other news The Penguins of Madagascar is due for release in the US tomorrow. We caught a special preview screening in the UK (review coming soon) and it was fantastic fun with Benedict having a riot as Agent Classified – the wolf. You can see several Penguins of Madagascar videos here.