The BBC Press Office is offering up interviews of David Tennant and Billie Piper in their Press Kit for Doctor Who: The Christmas Invasion along with a story summery of the special (which we previously reported here (warning: it contains possible spoilers)).
David Tennant, a life-long fan of Doctor Who comments about the The Christmas Invasion:
"The regeneration process is a severe biological process which takes a fair bit of time. This is not good news for Rose and the rest of the world, because whilst he's going through this, the Earth is being invaded by the Sycorax."
He continues: "It's a very difficult time for Rose. He hadn't prepared her for the changes he'd undergo. So whilst the Doctor is recuperating, Rose is trying to fathom out how she can save the world."
"She's also trying to understand how she feels about him now."
"The Christmas episode is a new start for the Doctor and Rose. They've got to rediscover each other and decipher whether they still feel the same about one another. Despite the new face, he is fundamentally the same bloke, he's still the Doctor and still has a huge amount of affection for her."
"However, it's not just the way he looks or the way he talks that is different. The Doctor's outlook on life has changed, as has the way he tackles situations. I think he's just hoping Rose can accept the changes and they can pick up where they left off."
The Christmas Invasion sees Billie Piper return as Rose Tyler:
"Rose feels so unloved and isolated at the start of the episode," Billie explains.
"She's returned home to her mother and Mickey and as ever they are there for her. But she feels like she's lost her best friend. The earth is being invaded and Rose has no control over the situation."
"The Doctor, who is still going through the regeneration process, isn't there to give her the answers and she's scared."