Antimatter should exist in equal amounts to ordinary matter, according to the equations Paul Dirac wrote in 1928, yet the universe around us is built almost entirely from one side of that pair. The film tracks the search for what happened to the missing half, opening with a shuttle crew at Kennedy Space Center loading Endeavour's cargo bay with the Alpha Magnetic Spectrometer, an instrument built to catch charged cosmic rays rather than the light that ordinary telescopes collect. Physicists Masaki Hori of Tokyo University and Jeffrey Hangst of Aarhus University explain how the Standard Model describes matter and antimatter annihilating each other in the universe's first seconds, leaving only about one particle in a billion behind to form stars, planets, and everything else. The film also brings in the Fermi Gamma Ray Space Telescope's detection of an antimatter plume near the galactic center, likely produced by a supermassive black hole, as evidence that antimatter has not vanished entirely. The open question driving the film: why does a matter-dominated universe exist at all, and where, if anywhere, did its antimatter twin go.