Captain Phillips,” the new nautical thriller starring Tom Hanks and directed by Paul Greengrass, is structured very peculiarly. For the past few hours, since seeing it with my son, I’ve been trying to figure out the significance of this oddity.

The film opens on Phillips as he prepares to leave for his latest gig: captaining a ship headed from Oman to Kenya by way of Djibouti. There’s some business with his wife (Catherine Keener, wasted here) intended to establish her and their children as objects of concern and to establish the theme of anxiety about globalization and increased competition – these bits are handled very bluntly, clearly intended to simply be gotten out of the way.

We’re then introduced to the pirates, and there’s a certain amount of parallelism clearly intended. A low-level pirate leader – Muse, played with both electricity and complexity by Barkhad Abdi – is roused from a sullen stupor by his boss, a flunky of a local warlord. He should be at sea, earning his living. And so he must choose his team from the desperately threadbare throng on the beach. He’s no more the master of his fate than Phillips, nor does he know his crew much better than Phillips knows his.

So far, so well established. Aboard ship, Phillips is concerned about the threat of piracy before it materializes. And, coincidentally, the pirates first show up in the middle of a drill he’s organized to get the ship into better fighting trim. They manage to ditch the pirates at first, but Muse, particularly reckless and particularly hungry, comes back the next day in his solitary skiff to take down the mammoth ship. He successfully boards the Maersk Alabama, and announces, “I’m the captain now.”

And now we’re in thriller territory. Before the pirates board, Phillips has already taken precautions to protect his crew. Now we’re going to see how well he outwits the pirates, whether he can keep them either from moving the ship to Somalia or killing him or any of his crew until the U.S. Navy arrives on the scene.

Which is precisely what we do see. We see just how well-trained Captain Phillips and his crew are, notwithstanding their lack of time working together and the griping we’ve seen previously. Over and over, they get the better of the pirates, until finally the crew captures Muse himself. They offer to trade him for their Captain, and let the pirates go free if they will leave the ship.

And then, as they are leaving in the lifeboat, the pirates contrive to kidnap captain Phillips, to salvage some of their catch’s value.

Now, this is all pretty standard thriller construction. After the villain’s plans have been foiled, it’s a pretty cliche move for the villain to kidnap either the protagonist or the person the protagonist values most – wife, girlfriend, child – in a last-ditch attempt to snatch victory from the jaws of defeat. “Speed” was the film that came first to my mind, but there must be dozens of examples.

The difference here is that this last ditch move happens at the midpoint of the film, with an hour to go, not twenty minutes before the end. That’s the structural oddity.

This turns the film into a diptych, and the two halves are very different films – indeed, they have different protagonists. In part one, we are “with” Captain Phillips, and the Somali pirates, howsoever comprehensible their motivations, are the antagonists he’s battling. Phillips is consistently active – and his actions are driving the story. (That’s not to say his actions are always correct – or that they always lead to positive outcomes. He made a number of decisions that, I think, can be questioned in hindsight – but that isn’t the point. Whether his choices are good or bad, they are driving the narrative.)

Moreover, he’s the underdog. Although the has the advantage of knowing the ship, and he also has the hidden advantage of numbers, the Somalis are armed, and he and his crew are not. He is their captive; Muse is the new captain.

In the lifeboat, this all turns upside down. Phillips continues to take actions of various kinds – he gives advice to Muse, he treats the wounded foot of a teenage pirate; he even manages to escape from the lifeboat at one point and tries to swim. But his actions don’t drive the plot, such as it is. He isn’t actually able to affect anything. And he isn’t really the protagonist anymore.

The protagonist, now, is Muse, the leader of the Somali band of four. And the situation is more like “Dog Day Afternoon” than “Speed.” Muse made this desperate move to try to salvage some value from his ill-fated expedition. But the choice to kidnap Phillips is actually what has trapped him. The U.S. Navy is on its way, and arrives in fairly short order after the lifeboat has launched. They would not be bothering if they had not taken an American hostage. And now that they’ve arrived, there’s no possible end-game that works out well for the Somalis. With advantages in every area – numbers, firepower, communications, maneuverability, basic supplies of food and water, you name it – the U.S. Navy is guaranteed victory. Muse and his crew may live as prisoners or they may die; they may let Phillips live or they may kill him. But they aren’t going to get paid. They aren’t even going to get away.

Muse’s role is to writhe in this trap, trying to keep himself from full realization of the futility of his actions, and trying to keep his men – or, rather, one especially hot-headed fellow, played by Barkhad Abdirahman – from killing Phillips and ending all doubt about their fate. Muse, then, is the one who can affect the outcome, with respect to Phillips and with respect to himself. As it happens, he’s the only one who survives, because he allows himself to believe one of the Navy’s lies just enough to let him escape from death and accept imprisonment.

We’re with Muse all through this portion of the movie, much more than with Phillips, notwithstanding all the cuts back to Hanks’s well-known face. That doesn’t mean we think Muse has become the good guy. He’s still a pirate; he’s not just a fisherman, as Hanks retorts at one point. But we are with him, emotionally. When he survives, we’re relieved; when he shows, on his face, that he already knew his fellows had all been killed, we feel his guilt.

So, as I say, I’ve been trying to figure out the significance of this surprising structural choice. Because it was unquestionably a deliberate choice; it would have been trivial to write the script in such a way that the last hour of the film was condensed to twenty minutes, and the period of thwarting the pirates on the cargo ship extended by twenty minutes, and there you have it: a solid 1 hour and 45 minute thriller with a classic structure. Greengrass chose, very deliberately, to take us from one kind of movie to another. Why?

Well, if he’d followed the classic thriller structure, this movie would have been a celebration of the triumph of Americanism, a straight line connecting the resourcefulness of captain Phillips in to the overwhelming power of the U.S. Navy. Meanwhile, if he’d made a film more like “Dog Day Afternoon,” we would have been “with” the pirates all along. But this isn’t 1975, and my guess is that neither Greengrass nor his audience is particularly receptive to a brief for outright disorder. Which is what such a film would be.

The structure he’s chosen, which takes real risks in terms of pacing, allows him to draw that straight line between Captain Phillips’s resourcefulness and the might of the U.S. Navy, while also showing what, and who, lies on the other side of that line.

A minority of critics who have expressed reservations about the film have connected it to “Zero Dark Thirty.” As a defender of the latter film, I both agree that there’s a kinship and am unsurprised that some of what I saw as a fruitful ambiguity in “Captain Phillips,” as in “ZDT” is being parsed in ways I find a bit off. This isn’t a movie “about” globalization or capitalism – or, rather, any theory about why there are haves and have-nots in the world is an imposition from outside the frame of the movie. This is just a film that does a very good job of showing us that global power imbalance – and, while not denying that the filmmaker and his audience are probably mostly on the side of power, letting us know what that imbalance feels like from both sides in a real-world confrontation.