At the center of the Milky Way, some 26,000 light years away, sits a source of radio noise first picked up by Bell Labs engineer Karl Jansky in the 1930s while he was hunting for static interfering with transatlantic phone calls. He traced the hiss to the constellation Sagittarius and moved on, and the signal sat unexplained for three decades until Erik Becklin used a borrowed military infrared detector to see through the dust obscuring the galactic core. This BBC Horizon film follows the astronomers who took up the search after him: Reinhardt Genzel's team in Chile and Becklin's collaborator Andrea Ghez at Hawaii's Keck Telescope, both tracking individual stars whipping around an invisible point to prove something impossibly massive and compact sits there. The film extends the same method to M87, a galaxy 50 million light years away, where Hubble observations of a billion-star elliptical turn up the same signature. The case for supermassive black holes, and their role in shaping galaxies, is built entirely from these decades of indirect measurement.