Around 1950, my future stepmother was my father's young secretary. His office was on the top floor of an old building in the heart of the City of London, reached only by a narrow staircase.
One evening, she stayed on alone to catch up with back work. My father was still a total stranger to her. He had left the office, locking the street door from the outside, and the building was empty except for her.
Many years later, she told me how she had been busy typing when she glanced up and saw a young man smiling at her, his hand still on the open office door knob as though he had just entered. "One moment." she said and looked back down at what she was typing. Looking up again there was nobody there and the door was closed.
Terrified, she rushed out of the building: the external entrance to the building was firmly closed as my father had left it. She rushed home and her mother was shocked by her white face and trembling body. She was quite ill with fear.
A couple of years passed, during this time my parents separated and he married her. One day, he pulled out an old photograph album of his own family and she immediately recognized the face of the man she had seen in the office two years before. It was my father's younger brother, who had been killed by a direct bombshell in Croydon when just eighteen.
She told my father her story of two years previously and he said with great serenity "Yes, I sometimes see him in exactly the position you described and the image brings me great comfort."