What is the alias of the person Clive leaves a letter for?
On the day that France surrenders to Nazi Germany in 1940, Prudence "Pru" Cathaway a strong-willed young woman from the upper class, joins the Women's Auxiliary Air Force, a military organisation linked to the Royal Air Force, to her family's surprise. Her aunt Iris and uncle Wilbur disapprove since she has chosen to serve as a private rather than as an officer. However, family butler Parsons privately expresses his support.
She goes off to training camp, where she makes friends with fellow WAAF Violet Worthing. As a favor to Violet, Prudence agrees to go on a double date one night; she is paired with Clive Briggs, a moody mysterious man with a dark secret. He seems to her rather bitter about something and is indifferent, even hostile, to her aristocratic background, but she likes him, and he asks her out again. Romance blooms.
On a holiday together on the southern coast, Pru twice overhears Clive talking in his sleep. The second time, she wakes him up, but he does not want to talk about it. Then his friend Monty shows up. When the three go to dinner, Pru learns from Monty that Clive is up for a Distinguished Conduct Medal for his actions during the Dunkirk evacuation. While Pru is dancing with someone else, Monty pleads with Clive to return with him. He was given a month's sick leave, but that was over two months ago, and he is about to be posted as a deserter. 
Finally, Clive tells Pru, indirectly, about his predicament and that he no longer wants to fight for the benefit of an English elite that oppresses and humiliates people of his class. Pru makes an impassioned plea for all the good things that England represents, but when she wakes up the next morning, Clive has gone, leaving her a letter of goodbye.
Pru