The Demon Lover - S1.E8

Kathleen Drover and her family have closed their London house and relocated to the countryside for the duration of the war. It's 1941 and relatively speaking, all is well. She is happily married and her now adult son is in love with wonderful young woman. This leads her to reminisce about her own first love, a dashing RAF pilot who was killed in 1916. Visiting her London house to collect some personal items, she is shocked to find a note, apparently written by her long dead lover.