are scientists. The affected personnel – manifestations of the Doctor, Clara, and the "scientists'" minds – attack and kill Professor Albert. The Doctor, Clara, and the "scientists" dream of Santa, who wakes them up to their real lives, one by one, until only Clara is left. Upon waking, the Doctor traces the psychic signal linking their dreams back to Clara. He pulls the crab off, and learns that Clara is now an elderly woman. The Doctor regrets not coming back sooner, when Santa appears. Realising that he is still dreaming, the Doctor wakes up again. He frees Clara, still a young adult, from the crab. Offering her all of time and space, the Doctor implores Clara to join him. Clara accepts. Continuity When the Doctor visits the elderly Clara, he helps her open a Christmas cracker, returning the favour she did for the Eleventh Doctor in "The Time of the Doctor" (2013) when he was too weak to pull a cracker open by himself. Production Casting In September 2014 announcements were made for a number of the guest cast, including Michael Troughton, Nick Frost, Nathan McMullen, Natalie Gumede and Faye Marsay. Michael Troughton is the younger son of Patrick Troughton, who played the Second Doctor from 1966 to 1969, and the younger brother of David Troughton, who appeared in The War Games, The Curse of Peladon, and "Midnight". There were numerous rumours circulating that the special would be Jenna Coleman's last on the show. Coleman and lead writer Steven Moffat remained quiet on the issue and insisted that people watch the episode to see whether she would be continuing into the ninth series. During the episode's climax, Clara decides to continue travelling with the Doctor, and Moffat revealed following the episode's airing that Coleman would appear in all of the ninth series. According to Moffat, Coleman was "to-ing and fro-ing" over her future in the series before ultimately deciding to continue. In a 2018 interview, Moffat confirmed that the script for "Last Christmas" originally contained Clara's exit from the series; Coleman reversed her decision to leave following the first read-through, and the episode's ending was subsequently re-written to allow the character to continue. Marsay's character of Shona was considered by Moffat to be Coleman's replacement as the companion for the ninth series, though nothing was fully formed. With Coleman electing to stay on the show, this would mark Marsay's only