Trama

The Tenth Doctor meets one of his previous incarnations.

After Martha Jones leaves the Tardis, the Tenth Doctor encounters his former self. As his former self figures out who he is the Tenth rambles on about how much he loved being that incarnation. The Fifth Doctor disappears back to his own time as the Titanic crashes into the Tardis leading into the next story 'Voyage of the Damned'.—Ben

The episode takes place within the final scene of Last of the Time Lords. After the Tenth Doctor (David Tennant) parts ways with Martha (Freema Agyeman), he tries taking off, only for the TARDIS to spin wildly and sound an alarm. Checking out the systems, the Doctor passes the fifth incarnation (Peter Davison) doing the same thing. The Tenth Doctor recognises his past self and is overjoyed to see him, gently poking fun of his particular eccentricities, such as the unneeded glasses he sometimes wears. The Fifth Doctor is annoyed, believing his counterpart to be a fan who has broken into the TARDIS.

The Fifth Doctor discovers that two TARDISes have merged, a paradox that will cause a massive black hole. The Tenth Doctor counters it with a supernova, a solution he remembers seeing himself perform in this same incident (a predestination paradox); the Fifth Doctor realises that the Tenth really is his future self. The Tenth reminisces as the Fifth begins to fade into a separate timeline:

You know, I loved being you. Back when I first started, at the very beginning, I was always trying to be old and grumpy and importantlike you do, when you're young. And then I was you, and it was all dashing about and playing cricket and my voice going all squeaky when I shouted. I still do that, the voice thing, I got that from you. Oh, and the trainers. And... [putting his glasses on] snap! 'Cos you know what, Doctor? You were my Doctor.

The two Doctors say goodbye: "To days to come," says the Fifth, raising his hat. "All my love to long ago," replies the Tenth with a bow. As the time streams split, the Fifth Doctor calls out, warning the Tenth to put his shields up. But it is too late; the Titanic collides with the TARDIS, leading the narrative into Voyage of the Damned.