Sky Silvestry

Sky Silvestry is a passenger and a businesswoman abord a tourist craft. She turns the Doctor's greatest strengths against him. She is the main villain, which hints that she may be an agent of another force...

In the episode trailer, she was seen to be backing against a wall shouting "It's coming for me", suggesting that the episode's monster is telepathic or she is being hunted by this monster and recognised the banging. (DW: Midnight)