Inspired by an eerie video that became an Internet sensation, The Tag-Along emerged out of nowhere to become one of the most popular horror films in Taiwanese history. In the viral video, a ghostly young girl in red can be seen following a group of hikers up a mountain path, shortly before the hikers meet with disaster. Is this a sighting of a mo-sien, a mountain demon who preys on fear? Cheng Wei-hao's feature debut lulls the audience with a setup taken straight from the rom-com playbook: Wei is a young real-estate broker who works too much and can't convince his quirky girlfriend to get married. But things take a dark turn when Wei's grandmother disappears, and the only evidence is the girl in red who mysteriously appears on the surveillance footage. The Tag-Along jolts your heart with the requisite frights and starts, but it also taps into your head by revealing the devastating regret that can result from taking loved ones for granted.