Watched by the world, the Metropolitan Police follow the radioactive trail of polonium across London, leading them to their main suspects, Lugovoy and Kovtun.

A team of detectives led by Timmons's "best man," Brian Tarpey, arrives in Moscow to interview the prime suspects behind Litvinenko's murder.

With their investigation complete, Timmons's team submit their file to the Crown Prosecution Service, which charges Lugovoy and Kovtun with Litvinenko's murder.