Cooper (Matthew McConaughy) and Amelia (Anne Hathaway) are on Miller's Planet in a faraway galaxy accessible only through a wormhole near Saturn. This planet is, as far as we can see, full of water, and revolves around Gargantua, a collapsed star. Giant tidal waves manipulated by Gargantua have rendered the planet inhospitable, and Cooper's and Amelia's mission unsuccessful. This is only the first mission in the film, so you might think that is fine.
You would be wrong. You see, while the failure of the mission increased their stay on the planet by only an hour, back on Enduranc....