The Double Shadow is about memory: the way it shapes you, makes you and sometimes breaks you. It follows the lives of two families in the lead up to World War II, each haunted by memory in different ways. The Rubens are rich but miserable, thanks largely to Arnold Ruben's overpowering obsession with creating a memory machine, a device that will allow the user to wipe away bad memories and live forever in happy ones. His daughter, Amaryllis, is deeply affected by the fact that she herself has no memory of the time before she was eight. The Pascoes, on the other hand, are poor but loving, their contentment occasionally interrupted by Mr Pascoe's withdrawals into the vivid memories of his battle experiences in World War I.The way the two families fates become intertwined is central to the story, but The Double Shadow is one of those books where the less you know going into it, the better. Because the way the story is slowly unravelled, skipping back and forth in time and between character's viewpoints, makes for a fascinating and gripping mystery. It's based on a a truly unique premise, something which can't be said too often these days, and which is thankfully followed through by accomplished world-building and a powerful sense of setting.The extensive cast of characters are also superbly drawn and well-developed. It's hard to know at first who to trust and who to like, but this ambiguity only makes them all the more intriguing. Through her exploration of memory and emotions - and the way the two are so often intertwined - Gardner gives the reader insight into why her characters (and, by extension, people in general) act the way they do, so even the most despicable characters evoke some empathy, if not any sympathy.The Double Shadow is a fanciful and thrilling example of what is so wonderful about stories; it transports you to another time and place so effectively, it makes you sit up and think, "THIS is why I read."