Mark Gatiss is back on writing duties for Saturday night's instalment of Doctor Who, the chilling 'Sleep No More'.
In a unique experiment for the series, the entire episode is told in 'found footage' style, aping horror favourites like The Blair Witch Project and Cloverfield.
What to Read Next
'Sleep No More' though is set in deep space - with the 'footage' recovered from the wreckage of the Le Verrier Space Station.
Reece Shearsmith makes a guest appearance as Rassmussen - a professor who's almost eliminated the human body's need to slumber.
But has his invention, the Morpheus Machine, spawned something truly terrible in the process?
"I'm delighted to be writing again for Peter and Jenna's brilliant TARDIS team and very excited about this particular story - it's been brewing in the dark recesses of my mind for a while now!" Gatiss said.
"I'm also chuffed to bits to finally welcome my old friend Reece Shearsmith onto the show. He's been badgering me for 10 years!"
But what are the true motivations of Shearsmith's Rassmussen? Can the Doctor (Peter Capaldi) and Clara (Jenna Coleman) trust the Le Verrier crew?
Only four sleeps left till you find out...
Doctor Who continues on Saturday (November 14) at 8.15pm on BBC One.
