Physicist Brian Cox tracks the science of nuclear fusion, the process that powers stars and could one day provide near-limitless clean energy on Earth. The film starts with Isaac Newton's work on the light spectrum and Einstein's mass-energy equation, then turns to the Trinity test site, where the same physics was first weaponized in the hydrogen bomb. From there Cox follows the decades-long effort to tame that power rather than detonate it, visiting the reactors and research teams attempting to confine plasma hot enough to fuse atoms and sustain the reaction long enough to produce more energy than it consumes. Interviews with scientists working on current fusion projects lay out why the engineering problem is so stubborn, from magnetic confinement to the sheer temperatures involved, and what a working reactor would mean for the world's energy supply. The film treats fusion as both a physics story and an engineering race, closing on how close, or far, that self-sustaining artificial star actually is.