The ceillist (Gabriel Allon #21)

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 president finally manages to cross Orlov's name off his kill list.
Before him was the receiver from his landline telephone, a half-drunk glass of red wine, and a stack of documents....