As we ponder just who Billie Piper could be playing now (oh, we have theories ), below, we take a look at 10 episodes (all streaming on HBO Max) you should watch now that she’s back on Doctor Who. This episode and one word (“Run”) are what started it all.

Ncuti Gatwa's Doctor Who exit brought back a familiar face to the TARDIS, but didn't explain how and why Billie Piper returned to the show.

The season finale of Doctor Who, ‘The Reality War,’ was shocking for many reasons. However, the biggest surprise involved an appearance by actress Billie Piper, who played Ninth and Tenth Doctor companion Rose Tyler.