Mark Gatiss has dropped some hints about his forthcoming episode of Doctor Who in an interview with Doctor Who Magazine.  Gatiss confirms that his episode was called What Are Little Boys Made Of? but says…

It probably won’t be now, because that’s a little too long … We’re toying with House Call at the moment, though that’s not very scary, is it? I’d like to call it Night Terrors …

He reveals that the story focuses on a little boy called George…

…who is frightened of everything. He has a nervous cough and a nervous blink, and he’s frightened of clowns, old toys, enclosed spaces, vans … and particularly of something being in the cupboard in his bedroom. And the Doctor turns up and tells him that he’s right! I can’t tell you anything more except that the monsters are the creepiest things ever.