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.

Doctor Who fans across the world were gagged on Saturday night when Billie Piper made an unexpected return to the franchise. After weeks of speculation about whether Ncuti Gatwa’s time as The Doctor was coming to an end in the not-too-distant future,