They Live imagines that class warfare and consumer culture are the machinations of undead-looking extraterrestrials; the aliens manage to walk amongst humans undetected, thanks to perception-altering signals with which they blanket the planet, and subliminal messages they've placed on billboards, magazines, and on television. Piper's character discovers special sunglasses that allow him to see past the deception, and he quickly becomes a fugitive.
The movie also includes one of the longest, most bizarre fight scenes ever committed to film. (I suppose if you're going to put a pro wrestler in your movie, you might as well have him wrestle.) Piper grapples with the indispensible Keith David for what feels like half an hour, even though it's really only about five minutes or so. See below.