Nian Yangxiao crosses over from a parallel world to rescue the woman he loves, who was murdered in another dimension. If she is killed in this world too, she will be lost for good. To stop it, he has to track down the killer, a woman identified by a mark on her thigh, before time runs out. Along the way he must contend with a number of gangs, helped by a newly gained ability to stop time. Across 20 episodes, the ONA blends action, fantasy, mystery, romance and drama around one man's race to save the person he cares about most.