Non-Stop Liam Neeson, Julianne Moore, Michelle Dockery. Directed by Jaume Collet-Serra. Rated PG-13. Opens Friday.

The reason that Liam Neeson has been so unexpectedly successful as an action star is that he’s completely convincing. He can stand in the middle of an airplane terrorized by an unknown villain, as he does in Non-Stop, giving a heartfelt speech about how he lost his daughter to cancer and became an alcoholic to deal with the pain, and the audience will totally buy every word of it. Neeson has been called upon to sell some pretty ludicrous nonsense in his action movies, and there’s plenty more of it in Non-Stop, which starts with some decent suspense before devolving into utter idiocy.

Director Jaume Collet-Serra also directed Neeson in 2011’s even more preposterous Unknown, and he has some slick stylistic moves here, swooping his camera around the New York-to-London flight that’s in the grip of a mysterious assailant, who taunts tormented air marshal Bill Marks (Neeson) and threatens to kill a passenger every 20 minutes. The movie’s first half is tense and sometimes surprising, but the more the villain’s convoluted plan progresses, the less convincing the movie becomes. Eventually, not even Neeson’s very particular set of skills is enough to pass off this far-fetched hokum as anything more than a dead-end trip.