Episode 7 details. SPOILERS

Episode 7: A Good Man Goes to War

 

Writer: Steven Moffat Director: Peter Hoar

Guest stars: Alex Kingston, Frances Barber, Christina Chong, Simon Fisher-Becker 

Want to find the most dangerous place in the universe? Easy. Harm a hair on Amy's head and just wait. But as the last of the Time Lords and the Lone Centurion blaze across galaxies to save the woman in both their lives, history is unfolding. In her cell, in Stormcage, River Song knows the time has come at last. She has a secret, and this is the day she tells it. 
The battle of Demons Run has begun. 
And the Doctor's darkest hour is now.


And Also from A Relative Dimension In Space
"The DW crew are busy filming at Cardiff City Hall today, with reports of soldiers with black shiny uniforms and berets on set (not UNIT). Another old 'friend' of the Doctor seems to be back too, but to avoid an immediate spoiler read it backwards to find out: llihcruhC"