In the early 1990s, two rival groups of astronomers set out to measure the universe's expansion by tracking Type Ia supernovae across deep space. One of them, the High-Z Supernova Search Team, expected to confirm that gravity was gradually slowing everything down. Instead the data pointed the opposite way: the expansion is speeding up. The film traces how that result forced physicists to accept that ordinary matter, stars, planets, gas, everything visible, accounts for only about five percent of what exists. The rest is split between dark matter, first inferred from the way galaxies rotate faster than their visible mass allows, and dark energy, the unexplained force behind the acceleration. Astronomers and cosmologists explain how supernova brightness works as a cosmic distance marker, why the two competing teams both arrived at the same startling conclusion, and what remains completely unknown about the substances that make up the bulk of the cosmos. It is a story about how much of reality is still unaccounted for.