Classic Doctor Who: The 10 Timey-Wimiest Episodes

10. The Ark (1966)

The Ark does something novel at the time--it takes place in two separate time frames. The TARDIS arrives on a giant space ark carrying humanity away from a planetary disaster, accompanied by nearly enslaved aliens known as Monoids. The Doctor's visit prompts a deadly disease to spread through both races, but after two episodes the Doctor puts things right and is on his way again.

But then we get the twist: the TARDIS returns to the ark hundreds of years later to find the political situation has reversed—humans are now enslaved to the Monoids. The Doctor now has to save humanity and help both races forge a future together.