Rod Blackhurst’s tense 2013 short film, Alone Time, in which a New York City woman named Ann (Rose Hemingway) heads upstate for a few days of camping by herself, was based on a true story. Fortunately, Blackhurst’s feature debut, Here Alone, is not. The gripping postapocalyptic thriller is set in what has become our standard vision of the near future, when a virus has decimated the world’s population, turning people into cannibalistic zombies. (Are there any other kind?) Ann (Lucy Walters) is doing her best to survive in the forest by herself, raiding nearby houses for canned food while evading the hungry walking dead. The film flashes back and forth between the present and the recent past, when Ann, her husband, Jason (Shane West), and their baby left their home to seek safety in the woods. Along the way, Jason taught Ann detailed survival methods, which she uses to the best of her ability. When she finds a teenage girl, Olivia (Gina Piersanti), and her injured stepfather, Chris (Adam David Thompson), in the middle of the road, she has to decide whether to help and trust them — while also facing haunting memories, as they remind her of the family she has lost — in a future that is uncertain for all of them. Director and editor Blackhurst, screenwriter David Ebeltoft, and cinematographer Adam McDaid (Ebeltoft cowrote Alone Time with Blackhurst, and McDaid photographed the short) have crafted a nifty little horror film, mining familiar genre territory but twisting conventions just enough to keep viewers on the edge of their seat. You can’t take your eyes off Walters (Shame, Power), who gives Ann a tough yet vulnerable quality, focusing on her troubled psyche, with Thompson (A Walk among the Tombstones, Mozart in the Jungle) and Piersanti (It Felt Like Love) keeping things right on the edge of comfort and chaos. Here Alone is screening in the Midnight section of the Tribeca Film Festival on April 24 at 9:45.