"Utopia" is the eleventh episode of the third series of the revived British science fiction television series Doctor Who. It was broadcast on BBC One on 16 June 2007. It is the first of three episodes that form a linked narrative, followed by "The Sound of Drums" and "Last of the Time Lords". The episode serves to re-introduce the Doctor's long time nemesis, the Master.

In this episode, former companion Jack Harkness (John Barrowman) jumps on the TARDIS, taking the Doctor (David Tennant) and Martha Jones (Freema Agyeman) to the planet of Malcassairo in the year 100 trillion, where a professor is working to send the last remnants of the human race to a place called "Utopia". The vicious Futurekind threaten to scuttle the rocket, but a greater threat hides in the shadows: the Doctor's greatest nemesis is about to rise again.

The TARDIS lands in Cardiff to refuel from the Cardiff Rift. The Doctor states that this will only take twenty seconds, noting that the Rift has been active recently. The Doctor sees Captain Jack Harkness racing towards the TARDIS and dematerialises. Jack grabs on to the outer shell, causing the TARDIS to fly to the end of the universe trying to shake him off. Upon arrival, a panicked Martha notes that Jack is dead. Several seconds later he revives and introduces himself to Martha. He tells them that he wanted to find the Doctor, so he returned to Earth using a vortex manipulator but was stranded in the 19th century. Jack decided to base himself at the Cardiff Rift and waited, knowing the Doctor would eventually land there to refuel. As they explore the planet they find an abandoned city and the Doctor notes that they are nearing the heat death of the universe. They encounter a lone human running for his life from the Futurekind, cannibalistic humanoids that are attempting to eat him. He is attempting to reach a nearby missile silo to get transport to "Utopia", the last hope of the human race.

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