Upon arriving at the university, Bill Potts saw the Twelfth Doctor and Nardole running through it. She secretly followed them, until they arrived at a mysterious vault. Bill accidentally made a noise while in the vault, so she left.
Later, the Doctor ran across the courtyard, with Bill after him, to check out that puddle. That evening, that same sentient puddle, taking the form of Heather, confronted Bill outside the university building, having chased Bill from her flat. She immediately ran up to the Doctor's study. (TV: The Pilot)