The main character is Ana, a child genius obsessed with palindromes and haunted by images of her future self falling to her death. Her father is a physicist who proposes a new theory of time (essentially, time is a wave passing back and forth through an eternally existing cause-effect series) and develops a technology which produces entropy reversal by deflecting the time wave in localised systems (e.g. to reverse tumour growth). He also discovers that the direction of time can be reversed in a person (travels in X-time): one can ride through one’s life backwards with awareness but seemingly without free will. One’s life can be thought of as a vinyl record playable forwards or backwards, the stylus being the moment of conscious awareness.
Aged 11, Ana is on holiday in Iceland with her parents. At the edge of a sea cliff, she breaks free from her mother’s arms and throws herself over the cliff to her death. Later, her grief-stricken mother becomes convinced that she can use her husband’s technology to travel backwards through her life and, at the moment on the cliff, stop her daughter from leaping.
She is successful, and in the second ‘layer’ of the book Ana lives, grows up and continues her father’s work. In doing so, Ana discovers that there is a further dimension to space-time (travels in Y-time). As time washes back and forth, each iteration – each layer of sediment – undergoes minute variations, some trivial, others changing the entire course of history. She sees that her mother relived the moment on the cliff hundreds of times before squeezing strongly enough to save her. She also discovers that the entire space-time structure is being eroded by some higher-dimension process, leaving strange columns, ‘chronostacks’. These erosion-resistant features are formed by moments of great emotional intensity in a person’s life, and are ultimately the last things to be erased.
She realizes that her fall from the cliff has created such a chronostack – getting a little higher each time she broke free of her mother’s grasp – and it will be the last place her consciousness can reside, while the rest of her life turns to dust around her. An epilogue hints that Ana may have ultimately escaped into Z-time.