I saw that one! It was basically this estate agent checking out a house and he heard a yelling for help and found David Tennant tied up in the attic and a shrine to him in one of the other rooms and Tennant did such a good job of conveying the terror that the poor bastard they were pranking was up to high doe too. The episode is here (http://www.youtube.com/watch?v=qxeQFWcHHf8), and that particular segment begins at around 27:30 :)

Also, yes a million times on the Mitchell/Brooker thing, especially the idea that there's this fondness and connection that goes beyond the mediocre sex...