Who’s next: End of an era as “Doctor Who” gets a new star

LONDON » For millions of Britons, a traditional Christmas Day includes turkey, brussels sprouts, Christmas pudding — and a special seasonal episode of “Doctor Who.”

The global success of the venerable sci-fi series means that fans around the world will also tune in Monday to watch Peter Capaldi’s final adventure as the space-hopping Time Lord known as the Doctor. (Americans can see it on BBC America at 9 p.m. Eastern).

The show has had a dozen Doctors over its 54-year history, and this is one of those bittersweet moments when one lead actor hands over to another. At episode’s end, viewers will see Capaldi transform — through a Time Lord process known as regeneration — into Jodie Whittaker, the first woman to play the part.

Before that comes a rollicking and poignant adventure that moves from the World War I trenches to the South Pole, features mysterious creatures made of glass and (of course) involves a jaunt in the Tardis, a timeand-space machine shaped like an old-fashioned British police phone box.

The episode loops back into the show’s own history, featuring an appearance by the very first Doctor, a white-haired gent who appeared on TV screens in 1963. He was played by William Hartnell, who died in 1975; David Bradley fills the role here.

Mark Gatiss, a regular writer for the show who guest stars in the episode as a British Army officer marooned in time, said there was “a valedictory feel” on the set of the finale.

“The sense of eras ending all over the place was very profound but at the same time it was actually a very happy experience,” Gatiss told The Associated Press in an interview.

Gatiss has loved “Doctor Who” since childhood and has written for it since 2005.

He’s better placed than almost anyone to explain the enduring allure