The series consultant has penned the episode which will see Stacey Branning (Lacey Turner) leave Albert Square after six and a half years. Speaking to Walford Web, Ashdown teased some of the other plots that will feature in the hour-long special.
"A bit of festive fun, but not too much," he revealed. "Some bad table manners at the Mitchell's. Alfie looking cuddly in his Santa suit."
Of Turner's exit plot, he added: "Stacey having to finally face up to the consequences of what she did to Archie a year ago. Max and Ryan having to make tough decisions. Janine resorting to desperate means to get what she wants. A dramatic exit."
EastEnders will broadcast on BBC One at 8pm on Christmas Day.
> Lacey Turner hints at 'Enders surprises