A chunk of a NYC subway disappears as WW III begins. Lost in another dimension, those train passengers find themselves stuck in a time loop. At the start of each cycle, they have 15 minutes to escape through portals before a huge explosion. As they evacuate, they teleport to random points in their pasts. There, they must locate and "tag" their younger doubles in order to return to the subway. Once back, they have just enough time to compare notes...