Video recovered from the wreckage of Le Verrier Space Station details how the Doctor and Clara became entangled in a rescue mission. As the footage plays out, a horrifying secret is uncovered, one that might threaten the life, sanity and species of anyone who watches.
I predict this episode will have fandom divided simply because it's a found-footage story. When told right, it has the potential to be very good. It's written by Mark Gatiss, so it could go either way.
Incidentally, because of the nature of the episode, this will be the first episode to not have the title sequence.