Doctor Who fans have been speculating that Steve John Shepherd would play the Doctor’s nemesis the Master but the big bad is actually Keeley Hawes, best known as Detective Inspector Lindsay Denton on Line of Duty.

“Anyone watching Jed Mercurio’s amazing Line of Duty will know that Keeley Hawes is having one hell of year,” executive producer Steven Moffat told the BBC. “And now it’s about to get even better as she achieves the greatest villainy yet attempted on Doctor Who: she plays a banker.”
Case closed Doctor Who big bad is Keeley Hawes
Ms. Delphox (Hawes) is “a powerful out of this world character with a dark secret.” Could it be that she’s a female Master? Moffat was reportedly considering a female Doctor despite the blacklash from some sexist Whovians.

“I am delighted to join Doctor Who and to be working with this incredible team,” said Hawes. “Ms Delphox is a great character and someone I’ve had a lot of fun playing.’