Elementary particles built the modern world, from X-ray machines to the internet, but physicists still cannot account for roughly 85 percent of the matter in the universe. This film follows researchers at DESY in Hamburg and at CERN's European Organization for Nuclear Research as they try to close that gap. Prof. Christian Schwanenberger and colleagues walk through underground tunnels and laboratories where light particles are fired through matter, an experiment that could point to a new, undiscovered elementary particle. The same imaging techniques used to hunt for dark matter turn up elsewhere: mapping the protein structure of viruses and scanning hidden cavities inside the Egyptian pyramids. Woven through the lab visits is the history of the field itself, tracing how Wilhelm Conrad Röntgen's discovery of X-rays and Peter Higgs's prediction of his named particle set the stage for today's search. The film treats dark matter less as a settled mystery than an open engineering problem, one being chased tunnel by tunnel and collision by collision.