Courtesy of tweets from fans containing set pictures, Capaldi and Mackie can be seen acting in period clothing, a recurring setting from the past several years, none more so than Capaldi's first ever episode Deep Breath back in 2014. The episode being filmed is understood to be Episode 3, written by Face The Raven's Sarah Dollard. More pictures and tweets can be seen below.
#PeterCapaldi spotted us filming him and came and said hello in style #drwho #bbc pic.twitter.com/vFGTQKExDu— Mark Llewellyn-Jones (@llewellyn_jones) August 1, 2016
Here's more #petercapaldi and #pearlmackie filming #drwho with #bbc @WalesOnline pic.twitter.com/0zGt5KR4zz— Mark Llewellyn-Jones (@llewellyn_jones) August 1, 2016