On the surface, “Gone Girl” is a high-polish thriller about a man who may or may not have killed his wife. But what it really is is an anatomy of a marriage, or perhaps more grandly, of marriage in general. It’s not a pretty sight.

Ben Affleck plays the husband who leaves his house on the morning of his fifth wedding anniversary to visit with his sister at a bar he owns. When he returns home, his indoor cat is roaming outside, a glass coffee table is smashed and overturned, and his wife is nowhere to be found.

As clues to a possible murder begin to add up, he predictably becomes the prime suspect. The inevitable media circus ensues.

This is one of those rare cases when Affleck is perfectly cast. There’s a natural insincerity to Affleck’s general demeanor that makes him a pretty limited actor but extremely well-suited to this role. It’s impossible for us to get a good read on his character in “Gone Girl” because Affleck doesn’t know how to fake sincerity. Everything he says or does comes off as phony or suspicious. In fact, director David Fincher has a lot of fun with a scene in which Affleck’s character is getting coaching lessons from his high-priced lawyer about how to act “earnestly” during a high-stakes TV interview.

Rosamund Pike as the missing wife has a complicated relationship with truth and honesty as well. Through a series of flashbacks and diary entries, we get a growing sense of just how much of a facade their marriage was.

The plot has a lot of twists and turns that are just about impossible to see coming. For a good hour of this two and a half hour movie, the audience is invested in finding out what happened (did he or didn’t he?). Much of that interest is dissipated in the second hour, thanks to a far too explicit explanation of what really did happen that anniversary morning. The final third of the movie is about whether the person (whoever that is) gets away with it.

The thriller aspect of “Gone Girl” is only partially successful because the “solution” to the mystery is far too elaborate and farfetched to be believable.

But what stays with you is its caustic take on marriage. The film opens and closes with a voiceover on what it calls “the primal questions of any marriage”: What are you thinking? What are you feeling? What have we done to each other?

“Gone Girl” is ultimately a very dark satire on the venerable institution of marriage.