Rachel Talalay, director of the two-part finale, has already promised that the end of the series eight will be full of "action" and "emotional material".
CLICK ON PHOTOS FOR GALLERY
Jenna Coleman pictured with the new Doctor, Peter Capaldi
"Both parts were written by Steven Moffat, which is fantastic," she revealed. "There's so much action and effects and emotional material. It's a Cyberman episode."
But a BBC spokesperson refused to comment on increasing reports that the Doctor's companion Clara Oswald would be leaving.
"It's speculation at this time," the spokeswomen told the Radio Times. "People will have to watch the series to see if she's coming back or not."
Jenna Coleman - with Matt Smith - has been playing companion Clara since 2012
It's an exciting week for Doctor Who fans – on Saturday Peter Capaldi will be seen making his debut as the twelfth incarnation of the Time Lord.
His casting was announced in August 2013 in a special live programme, following Matt Smith's decision to step down as the Doctor.
Jenna, 28, has been playing the companion since 2012, working alongside both Matt and Peter in the cult BBC series.