If “Serenity” were a book, it’d be the sort of trashy beach-ready thriller you’d read on a Kindle, so you’d be saved the raised eyebrows as a result of the embarrassing cover. But just like a book, you cannot judge this movie by appearances. Written and directed by Steven Knight, this would-be neo-noir at first appears to angle for “Key Largo” territory, but then swerves toward some forgotten ’80s pulp, before taking a whiplash-inducing hard left into something else entirely. I can’t recommend it exactly, but I want everyone to see it and discuss how insane it is with me.

For those that do venture into its crazy world, you’ll spend the first half the movie wondering why Anne HathawayMatthew McConaughey, Diane Lane, Jason Clarke, and Djimon Hounsou would have said yes to Knight’s script filled with stilted dialogue and wooden characters. Eventually, you’ll understand why, but you still won’t know if it was a good career decision or not, just as you’re not really sure if you’ve made the right choice in watching it. You’ll spend the rest of the movie just giggling and muttering, “WTF?” over and over again to yourself. “Serenity” is the least aptly named film of all time; there is a lot packed into its 103 minutes, but not a second of it is calming or peaceful for the audience.

But the title isn’t just ironic; it refers to the boat owned by Baker Dill (McConaughey), a fisherman on the remote, tiny island of Plymouth. And like in a garbage version of “The Old Man and the Sea,” Dill is obsessed with catching a fish, but instead of a marlin, here it’s a giant tuna that he’s seeking named . . . “Justice.” His obsession drives him to financial ruin, and he pushes his first mate Duke (Hounsou) away for his friend’s own sake as he continues to take Serenity out to the open ocean, wasting gas and time. His ex-wife Karen (a blonde Hathaway in Veronica Lake mode) shows up randomly, offering him $10 million to take her abusive husband, Frank (Clark), out on the boat and push him overboard to become shark food. Dill is conflicted, but there’s more going on than is initially clear.

“Sometimes we do bad things for good reasons,” Dill says, elucidating one of the film’s themes a bit too clearly, but going into the other would risk spoiling the fun. On the surface, “Serenity” initially appears calm, but there’s a serious riptide swirling underneath the waves, threatening to drown everyone involved. Knight previously wrote and directed “Redemption” and “Locke,” but he’s more famous as a screenwriter who ranges from critical hits like “Eastern Promises” and “Dirty Pretty Things” to messes like “Seventh Son” and “Burnt.” “Serenity” falls somewhere in between, aiming high but achieving lackluster results, especially if you give it too much thought. Knight is attempting a cheese soufflé with this one – an ambitious delight if well executed but absolutely lacking in anything nutritious – but what we’re left with on screen is a collapsed heap of fat. It’s still edible, but it’s not a meal you’d share on Instagram.

McConaughey is all in for that cheese. Given the choice to go big or go home, he definitely goes for the former with a giant performance that involves a lot of screaming at the sky and showing his ass, and I’m . . . not mad about it. He is on this movie’s silly wavelength and is fully committed to each moment, and Clarke takes a similar approach. Hathaway is clearly having fun with all this nonsense, playing a classic femme fatale and getting to say the script’s most deliciously ridiculous lines. Lane has a small, thankless role as Constance, the woman who shares Dill’s bed and helps him with his money problems. And with a shoot in Mauritius, I can’t really blame her for taking the part.

The oily slick of sin across the surface of this film isn’t what makes it wickedly fun; it’s the utter devotion to its bonkers twist, at once defying logic and good taste. “Serenity” knows it’s trash, but that’s not to say that it’s not entertaining trash.[C]