Alexander Litvinenko (David Tennant), a former Russian spy and Kremlin critic, dies in a London hospital bed, but not before accusing President Vladimir Putin of his murder. He had been poisoned with the deadliest substance known to man, and the police race to seal off contaminated sites, while detectives dive into a high-stakes murder investigation. In a dark world of political power games and fragile international relations, can the detectives find justice for Litvinenko’s devastated family?