Alexander Litvinenko, a former KGB officer turned Kremlin critic, dies in a London hospital in 2006 after drinking tea laced with radioactive polonium-210. The film follows the British police investigation that traces the poison's trail across London hotels, bars, and offices, using Geiger counters to map a radioactive path that leads back to two Russian suspects, Andrei Lugovoi and Dmitri Kovtun. Investigators, journalists, and people close to Litvinenko describe how the case unfolded in real time, from the mystery illness that baffled doctors to the eventual identification of a substance almost never used outside a nuclear reactor. The film lays out the public inquiry's conclusion that the killing was likely approved at the highest levels of the Russian state, and follows the diplomatic fallout between London and Moscow that followed. Interviews and reconstructed timelines keep the focus on the physical evidence, letting the polonium trail itself carry the case against a poisoning that turned an assassination into a public health scare across the city.