Sam Hurley and Bart Moore escape from prison, although Moore is seriously wounded in the breakout. They meet up with a confederate, a mute named "Dummy", and hide out in a ghost town. Along the way, they pick up several hostages, Kay Garven and her lover Arthur Ashton, reporter Larry Fleming, dancer Dorothy "Dottie" Vail, and the town's sole resident, Asa Tremaine. Sam calls Kay's husband Neal, a doctor, and threatens to kill Kay if he does not come and help Bart. Larry warns the gangsters that the government is going to conduct an atomic bomb test nearby the next morning, but Sam does not believe him. When Arthur causes trouble, Sam kills him without a qualm. To Kay's surprise, Neal still loves her enough to show up. He successfully operates on Bart, but warns Sam that moving his friend too soon will kill him. When Sam finally realizes that Larry was telling the truth, he still waits as long as possible to give Bart time to recuperate. Unknown to everyone, the test has been moved ahead an hour due to favorable weather conditions. When the five-minute warning sounds earlier than expected, Sam and Bart hurry to Neal's car and a desperate Kay persuades Sam to take her along. Larry overpowers Dummy, but the others drive away. Asa leads Dottie, Larry and Neal to safety in a nearby mine. Sam, Bart and Kay are killed by the explosion, but the others emerge unharmed.
When the film was released, The New York Timesfilm critic A.W. Weiler, while praising the cast, gave the film a mixed review, and at the same time encouraged first-time director Dick Powell. He wrote, "In making his directorial debut with Split Second, Dick Powell fortunately acquired a small but enthusiastic and competent cast, a fairly sturdy script and a contemporary peg on which to hang his melodrama, which turned up at the Criterion yesterday. Unfortunately, however, the pace at which this thriller moves is erratic and while its dénouement is spectacular it is hardly surprising. Split Second is a fairly taut adventure closely tied to the atomic age but it is rarely explosive... Mr. Powell's initial directorial effort is not likely to startle the cinema world but it is a long step in the right direction." More recently, film and DVD critic Jamie S. Rich, also gave the film a lukewarm review, writing, "The film doesn't have much tension, despite the inherent drama of the scenario. The main reason for this is Hurley. He isn't written as being all that menacing. He's more the know-it-all pessimist who sees through everyone else's charade, rather than the scary murderer who plays mind games with his victims. He stirs up the pot some, but the juiciest stuff emerges all on its own... the bulk of Split Second is essentially unremarkable. It's a serviceable lower-tier movie that moves at an efficient pace and provides mild entertainment."
