In a desolate alley on the bank of the Thames, a spy slips through the shadows. Mungo is the Director General of English intelligence, and he knows Moscow Centre has been watching him for weeks, but there is no spy in London better at losing a tail. Satisfied he hasn’t been followed, he drops off his message and disappears into the night. It’s a classic scene of Cold War espionage, save for one detail: Mungo isn’t a spy at all. He’s a teenager, playing an epic game of make-believe.