First published 1951; paperback copy shown is from Penguin Books (UK) 1961.
"You enter a room, a street, a country road. You see a figure ahead of you, solid, three dimensional, brightly coloured. Moving and obeying all the laws of optics. Its clothing and posture is vaguely familiar. You hurry toward the figure for a closer view. It turns its head and - you are looking at yourself. Or rather a perfect mirror image of yourself only - there is no mirror. So, you know it is your double. And that frightens you, because tradition tells you that he who sees his own double is about to die..."
When the fragile and harmless Faustina Crayle is asked to leave yet another teaching position, this time at a prestigious boarding school for girls, she pleads to hear the true reason behind the dismissal. She is terrified by what she learns... girls and maids at the school have reported seeing her in two places at once, one body lapsing into lethargy while the other is seen walking down the stairs or sitting quietly in a chair.
A fellow school teacher mentions the strange case to her lover, Dr Basil Willing, a psychiatrist and detective. He is intrigued - even more so when a woman is murdered at the school. Faustina is miles away, holed up in a hotel in New York... yet a young student is adamant she saw Faustina speaking with the woman moments before her death.
McCloy turned the idea of the doppelgänger into a truly terrifying thing. As the novel nears its end the tension - and the terror - builds inexorably to a haunting climax and conclusion that is intriguing and plausible yet leaves an uneasy taste in your mouth. Rightly classed as one of McCloy's best novels, it kept me up late into the night, scared to turn off the light - and not many books have been able to do that!