White Matter follows Paul, a late twenties baby-faced man, who is on a mission to find and expose pedophiles - driven by his own dark history of abusing young boys. He asks his sister, Beth, for a photo of her 12-year-old son, Jack, to use as bait for online predators. Fearing for the worst, but hoping for the best, she lends Paul the photo. During their conversation, Paul receives texts from a potential predator going by the handle Charliee44. From here, the film intercuts between scenes of Paul's encounter with Charliee44 and Beth's evening with her family.