About 2/3rds of the episode should feature 10 and Rose during previously off-screen time during the episode "The Girl in the Fireplace." They will be interacting with holographic recreations of the historical record of the current doctor's current adventure (which is in the past of the 10 & Rose's location in the general time-wimey timeline.) Got all that? Good.
They will be attempting to gain some insight into whether or not they should try to save Madame de Pompadour.
Also, the current doctor's story will be set 10 years in his personal timeline after the last time we saw him, but he and his companion will be exactly the same with 1 minor costume change each and one minor set change to the TARDIS control room.
What a perfect valentine to the fans!!!
