Doctor Who may have regenerated as many times as the lead character, but its sense of legacy is evident in every episode. Because of the series’ 60-year history, whole characters can seem to be forgotten for decades and then re-emerge in a grand reveal. That isn’t just limited to characters — writers and directors are constantly returning to the franchise, as exhibited by Episode 3 of the new season, “Boom,” written by former showrunner (and writer of some of the most acclaimed episodes ever) Steven Moffat.
