John Cairncross was a British civil servant, literary scholar and Soviet spy later identified as the fifth member of the Cambridge spy ring.
John Cairncross
The Enigma Spy - An Autobiography
Century, 1997.
Klugmann had arranged for the two of us to meet in the evening at Regent's Park, a spacious and delightful spot close to the West End where, he probably calculated, we would not be recognized or disturbed...We made our way into a part of the grounds with a fair number of trees. It was still light, but there were not many people around. I noticed that Klugmann was not his usual smiling, chatty self. My instinct of unease was not mistaken, for suddenly there emerged from behind the trees a short, stocky figure aged around forty, whom Klugmann introduced to me as Otto. Thereupon, Klugmann promptly disappeared without even daring to give me a furtive look
The author is recalling the day in May, 1937 when he was 'looking forward to a pleasant stroll in a green setting', but found that he had been 'trapped into an appointment with the KGB.' At the time he was a junior employee at the Foreign Office; despite his misgivings about the USSR he would later agree to spy for them.
My first encounter with Otto lasted less than half an hour and ended with my agreeing to meet him again, but nothing more. I made my way out of the park, got home in a taxi, arriving in a disturbed condition, and took a strong glass of whisky...Naturally I was never told Otto's real name, but we now know he was Arnold Deutsch, one of a group of Soviet undercover agents...
Regent's Park seems to have been Otto's favourite spot for recruiting spies - see the Kim Philby entry for an identical episode three years earlier.