Physicist Brian Cox closes his three-part look at British scientific history by asking how much of discovery comes down to luck rather than design. He walks through moments when a stray observation or a failed experiment turned into something bigger, using archive footage, historical recreations, and visits to the labs and locations where the work happened. Cox talks with scientists and historians about the conditions that let an accident become a breakthrough: the trained eye that notices an anomaly, the willingness to chase a result nobody predicted, and the institutions that gave researchers room to fail. The film treats serendipity not as pure chance but as something scientists can be ready for, contrasting careful, hypothesis-driven research with the messier reality of how many landmark British discoveries actually unfolded. Running just under an hour, it closes out the series with a broader argument about the culture of curiosity that produced them, rather than a single triumphant tale.