"Do you believe in Santa Claus?" You might have an opinion after this year’s "Doctor Who" Christmas special.

Like all of Steven Moffat’s best writing, it’s a multilayered episode to be enjoyed by children and discussed between adults. There are moments where you’ll laugh at the humor (queue the slinkies), and moments to make you cry at the pathos.

It will be broadcast Christmas Day at 7 p.m. on BBC America, and available online the day after.

Moffat said cheerfully on a press call, despite fighting a cold, that he defines "Last Christmas" as a "big, optimistic show that does of course have monsters that want to commit genocide on the entire universe."

Who is the Doctor? He’s an alien Time Lord from Gallifrey who runs about the universe in a TARDIS time machine. He regenerates into a new body (whenever the show needs a new actor), which also brings a different version of the character. This will be Peter Capaldi’s first official Christmas since he took over the part in the last few seconds of 2013. Capaldi’s Doctor is older, grumpy and a disbeliever in myths and legends — including Santa Claus.

At the end of the latest series, the Doctor (Peter Capaldi) has broken up with his latest traveling companion, Clara Oswald (Jenna Coleman), leaving them both unhappy and misunderstanding each other. Clara is also grieving for the loss of her boyfriend, Danny Pink.

Hardly spoilers since it’s in the YouTube trailers, Santa and his two snarky elves land their sleigh on her rooftop. The Doctor appears, sneers at Santa and then takes Clara to a scientific base at the North Pole where there are aliens threatening the world (in typical "Doctor Who" fashion).

There are overtones of "The Gift of the Magi," by O. Henry, a rearing reindeer (hey-ho, Silver!), a touch of classic Dao­ism, a song from the glam-rock ’70s and a stellar score from the BBC National Orchestra of Wales.

"I wrote the last third of this Christmas special on the World Tour with Peter and Jenna," Moffat said of the international publicity tour of August. "So, my principal memory of that, which is now fond but at the time I slightly resented, was I’d be watching them all having a high old time in bars and pubs and cafes, and I’d be sitting by myself at a table in the corner trying to write ‘Doctor Who.’"

"In as far as writing (is) ever enjoyable, I think being able to write dialogue between the Doctor and Santa Claus is as good as it gets."