After the first-ever public screening of the movie Predestination, star Ethan Hawke stood on stage at Austin's Paramount Theatre Saturday night and explained his enthusiasm for time-travel movies like the one we had just seen to the South by Southwest Film Conference audience. "It's a genre where you can speak about challenging ideas without pretension," the actor with the close-cropped flattop and high cheekbones said. "A film like Her last year is a way to get us talking about ideas without actually mentioning the ideas." In Predestination, written and directed by the Australian brothers Michael and Peter Spierig, Hawke plays a "temporal agent," a government operative, who travels back and forth in time to prevent crimes before they happen. In the opening scene, his attempt to defuse a bomb in 1975 is foiled when the bomber starts shooting at him. Nonetheless Hawke has the bomb in a container and has almost closed the lid when it goes off. His face becomes a mask of flickering white flame, and he awakes weeks later as the doctors unwrap his bandages to reveal the sticked-together pieces of his head. He picks up a black fiddle case, dials in a new date and with a small thunderclap he's gone. We next see him as a hippie bartender in a Cleveland dive. He glances as his strange, black wristwatch that reads, "October 7, 1970." The skinny man at the bar bets $20 against a bottle of whiskey that he can tell Hawke the strangest story he's ever heard. The stranger wins the bet. Without giving too much away, let's just say that the stranger has undetermined gender, undetermined parentage and a lost child. Hawke hands the visitor the bottle of whiskey and invites him/her to join the Temporal Bureau's campaign to catch the "Fizzle" Bomber. The Spierig Brothers, who had directed Hawke in their earlier film, Daybreakers, create an alternate past that resembles the actual '50s, '60s, '70s and '80s but departs from recent history in intriguing ways. It's an almost-familiar world, like the one in Her. The Spierigs also do a good job of walking that thin line between explaining too much and explaining too little. We have enough information to follow the plot, but not enough to guess what will happen next. Sarah Snook, who plays the storytelling stranger, does a similarly nice job of letting us learn enough to care about him/her but hiding enough to sustain curiosity. Hawke's character has secrets of his own behind that mask of a Humphrey Bogart-like, film-noir private eye. The result is a wonderful brain teaser, a metaphysical puzzler that will keep many dorm lounges buzzing with conversation into the early hours of morning. But in the cause of maintaining the mystery, the film never makes clear what the two main characters really want and what they must overcome to get it. As a result, for all its cerebral dazzle, Predestination never makes us fear for the heroes.