Series 3 (2007)
Episode title: UtopiaFeaturing: Tenth Doctor
Companions: Martha Jones, Captain Jack Harkness
First shown: 16th June 2007
Related articles: The Master
Guide: The Doctor lands the TARDIS in Cardiff, Wales, so that he can do what he did in Boom Town (series 1 episode 11) - refuel the TARDIS on the rift energy. But as the Doctor prepares to go, someone jumps onto the outside of the TARDIS and clings on. The TARDIS doesn't like this, and throws the Doctor and Martha to the end of time. A time that no Time-Lord has ever been to.
When they step out of the TARDIS, Martha finds the body of the person who had clinged onto the TARDIS and gone through the time vortex with them. The Doctor tells her to leave him, but she insists on trying to help. As Martha pronounces him dead, he suddenly breaths a gasp of breath.
Captain Jack Harkness is back and ready for action. But the Doctor doesn't like him, but won't say why. The three of them start to explore the planet they've landed on, until they find a sanctary which is housing humans for safety from the future-kind.
The Doctor finds out that the planet they are on is dying, and the humans on it are preparing to leave, to Utopia. And Professor Yana is trying to build a rocket to get them there, but it doesn't work. His assitant Chantho is unable to find a fix for the broken system. But the Doctor does.
As the Doctor fixes the system, he needs someone to set up the pistons in the main room, which is filled with radioactive material, and no one can go in. Someone does try, and is killed, so they need a man who can't die.
Enter Captain Jack Harkness. As Jack tries to do the job for the Doctor, the Doctor watches, and explains that he's wrong. He explains why the TARDIS took them so far away from their time, because it was trying to get rid of Jack. But Jack is destined never to die.
Martha finds that Professor Yana has a fob watch, exactly the same as the one the Doctor had in episodes eight and nine (Human Nature and The Family of Blood). The Doctor says that's impossible, but when they get back to Yana, he's opened the fob watch, and is no longer Yana.
It turns out that Professor Yana was the Master, a time-lord like the Doctor, who had hidden himself as a human at the end of time to hide from the Time War.
The episode ends with the Master stealing the Doctor's TARDIS, after regenerating.
This is the first of a three part story. Read the second part here and the third part here.