Gerard Butler stars as a submarine captain who has to navigate a lot more than the perilous Russian waters. He’s the center of an elaborate (and somewhat improbable) plot to thwart a government coup. An unusual alliance results in some tense underwater threats and a bit of action, but never plumbs the depths of dramatic tension that would have made it a thriller. Despite the unlikely plot developments, it’s relatively entertaining and mildly engrossing.

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