'Serenity' review: A big fish story that stinks 

“Serenity” opens with Baker Dill, a fishing-boat captain played by a sun-dried Matthew McConaughey, trolling for tuna with a couple of tourists. When Baker hooks a fish, though, it turns out to be his personal Moby-Dick, and he refuses to hand the rod to his customers. They paid good money for this, they point out, but to no avail.

By the end of “Serenity,” you might feel the same way. In trailers and posters, “Serenity” has been pitched as a steamy noir set on a tropical island, but “Serenity” — named for Baker’s boat — is a massive bait and switch. Yes, there’s a gorgeous ex-wife, Karen (Anne Hathaway), who has married an abusive criminal, Frank (Jason Clarke), and now wants Baker to feed him to the sharks. Yes, there is bloodshed; there is also explicit sex that reveals more of McConaughey than we saw in even “Magic Mike.” Halfway through, however, “Serenity” becomes a whole new film with whole new themes — and new problems. Writer-director Steven Knight clearly cherishes his surprise twist, so I won’t spoil it, but imagine “Double Indemnity” turning into “The Truman Show” and you’ve got the idea.

It’s clear from the get-go that something is amiss. McConaughey is well cast as Baker, one of those wiry, sweaty, haunted types who gravitate toward edge-of-the-Earth islands like Plymouth, but his performance is cartoonish, overly jittery and intense, built around suspicious stares and a constantly click-clacking Zippo. Hathaway, as the femme fatale, presents oddly: a bleached blonde with jet-black eyebrows and a voice somewhere between husky and baby girlish. Clarke does what he can with Frank, a generic kingpin who likes to conflate sex with corporal punishment. The love-triangle set-up is such a classic that we’re willing to overlook the film’s odd tics, including the zig-zagging camerawork that comes with accompanying “swoosh” noises.

The weirdness, we’ll discover, is all intentional. As Baker debates whether to commit murder — not just for money but for his young son, who now lives under Frank’s rule — we begin to realize that Plymouth island holds a strange secret. When the truth finally dawns, it feels less like a mind-blower than a sucker punch. Knight, who once made a riveting, laser-focused thriller with just one actor (“Locke” starring Tom Hardy), here does the opposite, creating a scattered, unsatisfying mess with a full cast (including Diane Lane as Constance, Baker’s favorite sex worker).

As a wild-eyed Baker says near the movie’s end: “Nobody knows anything!” It’s the tagline that should have gone on the posters for this exasperating film.