I was about 75% of the way through Under the Skin the novel when I decided I couldn’t wait and needed to see the film. I was spellbound by it, though one scene toward the end bothered me because it seemed gratuitous. And then I finished the book and found that it contains a similar scene (though the scenes don’t end the same way). So there are some common threads between book and movie, but on the whole they’re as different as two stories can be. The bones of the premise are the same, the change that happens to the protagonist (“Isserley,” in the book; no one has a name in the movie) is roughly equivalent, and both end with the same imagery. Apart from that, they diverge in terms of plot, incident, theme, tone, setting, and of course verbosity. The book’s very interior, as books can be; the movie lives at the furthest extreme of exteriority.
The book concerns itself with questions about the difference between humans and animals and how we treat each of them; about the way we work (or don’t) and the role of class resentment and distrust in maintaining the status quo; about denial and repression; and about how making connections can save us and kill us. Apart from this last, the film has different interests: to the extent they’re decipherable, they seem to deal with the difference between manufactured and genuine humanity and the way in which utter amorality and budding compassion can both, in a sense, cut through the superficial and get to the heart of reality.
The book is almost too straightforward in expressing its themes, but it’s so vividly and soberly imagined, crafted with such attention to detail, and so generous to its characters that it turns a potential punchline or Twilight Zone-esque twist into a gradual, inevitable realization. It works very well, stumbling only a little toward the end, and would be my choice if I had to recommend one of the two. But the film is so remarkable in its way, so fascinatingly alien and opaque, reducing almost all its dialogue to the dull murmur of a foreign language one speaks but does not comprehend without effort, that it’s not to be missed.