The set up is this: Earth was invaded by a bunch of alien scavengers, or Scavs. We pretty much got rid of them by nuking the planet. Now Earth is mostly empty, all the people gone to live on Titan, leaving Tom Cruise and and Andrea Riseborough as caretakers and drone technicians living in a modernist Farnsworth house on a stalk above the clouds.
Life is good, with the elegant cloud lifestyle and the idyllic depopulated Earth at their feet. But Cruise keeps dreaming of a time before the invasion, and about Olga Kurylenko. This disturbs him, although I would find it rather pleasant (although I thought she was Noomi Rapace for the whole movie).
Soon he begins to find out that nothing he believes is true. Since he has his mind wiped clean (for reasons) every five years, it's pretty easy to fool him. Just like in Vanilla Sky, when something seems too good to be true, it's probably an artificial reality planted in your brain somehow.
I don't want to spoil the twist(s), although I sort of did, so I won't discuss the plot holes in detail. Except:
- Timeframe: This supposedly takes place less than 100 years after the invasion. Yet civilization is almost wiped from the earth - New York harbor is a meadow with the torch of the Statue of Liberty sticking out. Shouldn't it be like 1,000 years after invasion?
- Boomer-centricism: Cruise has feelings that bubble up through the mindwipes - a love for the simple true things of human culture, like 70s FM rock music. That's certainly universal, isn't it? (OK, he also gets into the poetry of Macaulay.)
I'd better say no more - except even if you don't buy the story, this is an incredibly beautiful movie. A lot of it is like the Iceland portion of Prometheus, lovely blue wilderness. Just enjoy.