DI Brent Hyatt and DS Chris Hoar are summoned to University College Hospital in Central London to interview a patient with an extraordinary story to tell. Before he passes, Alexander Litvinenko accuses President Vladimir Putin of murder. The investigators race to determine the cause of death.

The day after Litvinenko"s death, radiation teams swarm across London to secure potentially contaminated sites visited by the Russian spy. Officers discover traces of polonium at a sushi restaurant where Litvinenko met Mario Scaramella before a later encounter with Andrey Lugovoy and Dmitry Kovtun at the Millennium Hotel, which also tests positive for polonium.

A team of detectives led by Timmons"s "best man," Brian Tarpey, arrives in Moscow hoping to interview Lugovoy and Kovtun, now the prime suspects behind Litvinenko"s murder. The discussion, conducted in Russian, yields a few promising details. At Litvinenko"s funeral, his widow, Marina, receives updates on the investigation"s slow progress, prompting her to take matters into her own hands.

Their investigation now complete, Timmons"s team submit their file to the Crown Prosecution Service, which charges Lugovoy and Kovtun with Litvinenko"s murder. However, as the killers are safe in Russia and protected by Putin, the chances for true justice appear to be slim.