Peter Capaldis final episode of a long-running science fiction television series this holiday season will see Pearl Mackie reprising her role as Bill Potts...Review:The long-awaited final episode of this iconic science fiction series delivers a satisfying conclusion to Peter Capaldis run as the time-traveling protagonist. Pearl Mackies return as Bill Potts adds an extra layer of nostalgia and emotion to the journey. Fans of the series will not be disappointed with the dramatic twists and turns that unfold in this must-watch Christmas special.