Apr 24, 2017

from Wiki

The Doctor and Nardole have occupied themselves under the guise of a university professor and assistant. Bill Potts is called to the Doctor's office, where Bill becomes the Doctor's student. Bill becomes intrigued by a student named Heather. Heather asks her to inspect a puddle, asking her if she can see what's wrong with her reflection. The Doctor investigates the puddle, and notes that it is not a reflection, but something mimicking them. Bill returns to her flat, and is chased by a moving body of fluid: A living fluid from an alien ship that has absorbed Heather and her feelings for Bill. Bill runs to the Doctor's office and they flee into the TARDIS. The Doctor moves the TARDIS, where he and Nardole check on a vault they are guarding. The TARDIS lands again in Australia, where the Doctor admits who he is. The fluid follows them to another planet in the future, then through a Dalek battle, but survives. Bill convinces "Heather" to let her go, and it departs. The Doctor and Bill return to his office, where he attempts to wipe Bill's memories of the day but she stops him. As Bill leaves, she finds the Doctor waiting with the TARDIS.