This is the third in a sort-of series of stories in which the 10th Doctor (David Tennant) runs into one of his previous selves and they have an adventure together. In the first Out of Time, he and 4th Doctor (Tom Baker) battled the Daleks in a transtemporal abbey. In the second story, he joined the 5th Doctor (Peter Davison) jumping around different eras in Parisian history to stop a very long-term plot of the Cybermen.
This time, it’s the 6th Doctor (Colin Baker). The threat they face is the Weeping Angels.
The Tardis has been kicking up a fuss and, instead of taking the 10th Doctor where he wants to go, lands on Lucidus Silvara, a planet famed for being constantly in the blinding white light of its “thousand cold suns,” except for one day each year when there’s an eclipse and the beauty of the planet is visible briefly in the dim light. This is not that day. The Doctor cannot see the man who calls out to him from the bright light, but people who’ve watched the original Doctor Who series, or listened to these Big Finish audios, recognize that voice right away.
The 6th Doctor had dropped in to see the planet on its annual eclipse day, and doesn’t understand why it’s suddenly so bright again; the eclipse shouldn’t have ended for a few more hours. He’s lost his own Tardis somewhere around here, but of course can’t see where it is. But he soon realizes that he’s talking to the Doctor and not just a doctor, and who else would be in a position to lend a hand? (although he doesn’t care for the “grubby” look of Dr. 10’s Tardis).
The problem of what happened to Dr. 6 becomes apparent, when a Weeping Angel is discovered in the vicinity, coming toward them at “blink” intervals. The Weeping Angels can’t move when someone, even another Angel, is looking at them, but they can move very fast–in the blink of an eye–when that gaze is interrupted.
Actually, there are two of them, on either side of the Doctors.
Dr. 6: “Angel to the left us. Angel to the right.”
Dr. 10: “Here I am stuck in the middle with you.”
Dr. 6 [groaning]: “You’re not one of those Doctors, are you?”