The final episode of David Tennant has him battling both the Master and the returning Time Lords of Gallifrey. After defeating them, he knows his time for regeneration is soon so he travels back to see his recent companions one last time. The Timelords are returned back to where they had been during this time. They might make another appearance again in a future episode. He visits Captain Jack in a bar and gets him to introduce himself to Alonso, the surviving ships captain in Damned Voyage, Christmas episode some years ago.
Martha Jones has now hooked up with Mickey Smith and fighting aliens on what looks like a barren planet. He visits Rose before he meets her for the first time because shes currently in another dimension. The episode ends as he regenerates during an emergency into the new Matt Smith doctor. A preview of the new series is available on the Doctor Who Website. He's up against new aliens, old aliens (Daleks) and Vampires. Also whereas previous doctors have shied away from using guns, this time, he's seen with a gun. The first episode of the two part story drew an audience of 10 Million viewers.