About Doctor Who Season 7, Episode 4 : The Power of Three

The Doctor and the Ponds puzzle an unlikely invasion of Earth, as millions of sinister black cubes arrive overnight, almost like presents falling from the sky. But what are they, what Guest Stars: Karen Gillan, Arthur Darvill, Steven Berkoff, Mark Williams, Jemma Redgrave, Selva Rasalingam, Alice O'Connell, Peter Cartwright, David Beck, Daniel Beck, David Hartley,