Sometimes a movie comes out of nowhere and wins you over. Safety Not Guaranteed is that kind of unexpected gift. At first, the story smacks of quirk: A loner (Mark Duplass) places an ad for a partner to join him in traveling back in time (“Must bring your own weapons. Safety not guaranteed”). Tracking the story are Seattle journos Jeff (Jake Johnson), Arnau (Karan Soni) and Darius (Aubrey Plaza), who falls for the big guy. Director Colin Trevorrow and writer Derek Connolly keep the film humming with funny and touching surprises. And Plaza is a flat-out enchantress.