The BBC have released the synopsis for "Dark Water" - the first part of the two part finale which will air on BBC1 on Saturday 1 November 2014:
In the mysterious world of the Nethersphere, plans have been drawn up.
Missy is about to come face to face with the Doctor, and an impossible choice is looming.
“Death is not an end” promises the sinister organisation known only as 3W – but, as the Doctor and Clara discover, you might wish it was.
Written by Steven Moffat
Directed by Rachel Talalay
Guest stars Michele Gomez and Chris Addison