Lewis, fresh off Billions, and Pearce, who recently starred in Mare of Easttown, have begun production on the spy series based on Ben Macintyre’s book about notorious KGB double agent Kim Philby. Pearce will play Philby. Lewis will take on the role of Nicholas Elliott, Philby's close friend and MI6 colleague. "The show examines espionage through their friendship, the fallout of which affects East-West relations to this day," per Deadline. "Philby was a British spy who notoriously defected to the Soviet Union in the 1950s, betraying secrets to the Russians in the early years of the Cold War. He and Elliott entered the spy game together, but as they rose through the MI6 ranks, Philby turned double agent." The limited series is exec produced and directed by Nick Murphy.