Gravity is the force everyone assumes they understand until Brian Cox starts asking what it actually is. The particle physicist drives across the United States chasing the question, stopping at a Texas observatory where researchers fire lasers at retroreflectors left on the Moon by Apollo astronauts, using the returning light to measure the Earth-Moon distance down to millimeters and test whether gravity behaves exactly as Einstein predicted. Another stop takes him inside a maximum-security military installation to see instruments built to detect the bending of space and time itself. Cox threads these encounters with the history of the idea, from Newton's own uneasy religious reasoning about a force that acts at a distance with no visible mechanism, to Einstein's replacement of that mystery with curved spacetime. Scientists at each location explain what their equipment measures and why gravity keeps resisting a clean fit with quantum physics. The film stays anchored in physical demonstrations rather than abstraction, using Cox's stops as evidence for why a force this familiar remains one of physics' least settled problems.