The Tenth Doctor meets one of his previous incarnations.

When the hospital she works at is transported to the moon, medical student Martha Jones joins forces with The Doctor to hunt down an alien fugitive before the oxygen runs out

As Rose Tyler embarks upon her first big TARDIS adventure with the newly-regenerated Doctor, they discover a sinister hospital run by strange cat people and run in to two old acquaintances, The Face of Boe and Cassandra.

在第十任博士的故事里，他始终强烈的孤独。仿佛诅咒，他的同伴——所有的人总有一天离开他；自己并一个人地走向死亡。在他的生命最终结束的时候，坐着塔迪斯和过去的同伴一一告别。第十任是一个轻松健谈，随和机智的人，对敌人总会给予第二次机会却又绝不过分仁慈。曾经和女伴罗斯有过一场恋爱，最后以两人分隔在不同的宇宙告终，之后也和其它的同伴一起环游宇宙，拯救世界。第十任一般穿深褐色（蓝色条纹）或蓝色（铁锈红条纹）四个扣子的西装，衬衫和领带，浅棕色的人造麂皮大衣。

The TARDIS arrives on Androzani Minor, the source of a life-prolonging drug refined from a substance called spectrox. Production of the drug is controlled by Sharaz Jek, a facially deformed madman in self imposed exile, who blames Morgus, a powerful industrialist on Androzani Major, for all his misfortunes.
Jek is fighting government troops sent to liberate the drug. His weaponry is being supplied by gun-runners secretly employed by Morgus, who receives payment from Jek in refined spectrox. This gives Morgus a monopoly of the drug on Major.
Jek becomes infatuated with Peri, and saves her and the Doctor from being executed on Morgus's orders by government troops led by General Chellak. The two travellers escape after learning that they have contracted spectrox toxaemia, a fatal condition to which there is only one antidote - the milk from a queen bat, which the Doctor must obtain from the deep caves on Minor. Morgus, seeing his power base slipping away, travels to Minor.
In a climactic battle, Morgus, Jek and all the soldiers are killed. With moments to spare, the Doctor carries Peri back to the TARDIS, where he gives her all the milk that he has managed to collect. She recovers, but the Doctor has to regenerate to save his own life.