In 1908, a woman with no formal physics degree was cataloguing stars in a Harvard basement when she noticed something that would shatter our understanding of how big the universe actually is — and then watched a man take credit for it. This episode traces how Henrietta Swan Leavitt's discovery of the Cepheid variable star relationship became the ruler with which Edwin Hubble measured the cosmos, and asks an uncomfortable question: how many other fundamental breakthroughs are still attributed to the wrong person.