A Video was released in the US, for those that had pre-ordered Series 6 Part 2 on iTunes, and some of the stills from the video can be seen below:
A Cybership crashed underground a long time ago and a city (Colchester) has built up over it. The Cybermat is sneaking around a shop stealing electricity to bring the Cybermen back to life. Something about failed conversions. Matt’s wearing the long coat throughout.