This story contains MODERATE SPOILERS for episodes of “Doctor Who” that have not aired in the United States yet.

The final regular episode of “Doctor Who” until 2010 is so big, BBC has had to allot a bunch of extra time to fit it all in. The fourth season finale is clocking in at 65 minutes, nearly double the length of a normal episode, which will include appearances by actors from two of the “Doctor Who” spinoffs, as well as Billie Piper as Rose Tyler and Freema Agyeman as Martha Jones.

“Stolen Earth,” which served as the penultimate episode, had the Daleks and their creator, Davros, stealing the planet and then subjugating it. The Doctor, played by David Tennant, was shot and injured by a Dalek, and was in the process of regenerating when the cliffhanger hit. Although there’s been …