In 2011, physicists at the OPERA experiment announced a result that seemed to break physics: neutrinos that had apparently outrun light on a run between two underground labs. Marcus du Sautoy walks through what the anomaly actually measured and why a timing difference of a few dozen nanoseconds was enough to make headlines worldwide. He talks to the scientists who ran the experiment and the wider community that immediately set out to replicate or demolish the result, since a single measurement, however striking, does not overturn Einstein's relativity on its own. The film follows that process of checking, doubting, and re-checking rather than presenting the anomaly as settled fact, and lays out what it would mean for physics if faster-than-light travel really were possible. Du Sautoy keeps the explanations grounded in what the equipment could and could not actually detect, rather than treating the story as a mystery to be marveled at.