Matt Frei explores the poisoning of Russian Sergei Skripal and his daughter Yulia in Salisbury, searching for clues to potential motives that could explain why the former British double agent was targeted. The search takes him into the murky world of espionage, politics and crime, examining whether the latest chapter in a number of suspicious deaths of Russians on British soil could all be linked. The Kremlin denies it, but were these simply tragic endings or brazen state-sponsored assassinations?