Doctor Who Christmas Special 2011 ideas?

Well I just thought of a great idea for the Doctor Who Christmas special - I personally think it's quite a good idea considering i'm 13. David Tennant and Billie Piper return for one night only. Matt Smith (Doctor) could get a phone call from Rose Tyler, saying her Doctor, is in danger and being hunted down by Judoon but they can't come to earth can they so they send their hit man - who is going to capture David's doctor DEAD OR ALIVE! The hit man seems quite normal, and looks it, but he has a power, a strange and dangerous power. But there's a mix up and they capture the wrong doctor! It's then up to David's Doctor, Rose, Amy and Rory to save Matt's Doctor as the judges of Earth decide his fate! Good one hey!