The Doctor looked over to the creature and gave Jo a nod and smile that wasn't at all genuine.

"Oh, I've got this bloke here. By the time we get back to his time, Christmas won't be Christmas anymore, will it? Well, hard to tell, with time travel. I'm sure we'll find out."

He didn't want to leave this time period, but somethings...things worked out that way. They had to. The cost of staying now would be this being's life.