"Viktor Orlov had a longstanding appointment with death. Once Russia’s richest man, he now resides in splendid exile in London, where he has waged a tireless crusade against the authoritarian kleptocrats who have seized control of the Kremlin. His mansion in Chelsea’s exclusive Cheyne Walk is one of the most heavily protected private dwellings in London. Yet somehow, on a rainy summer evening, in the midst of a global pandemic, Russia’s vengeful...