The relationship in question is that of Lotto & Mathilde, madly in love and married at the tender age of twenty-two after knowing each other for all of two weeks. The first half of the book tells the story of their marriage from Lotto's point of view, and though the writing is utterly gorgeous and the characters dynamic and multi-dimensional, it's on the darker side, without much in the way of comic relief. The second half, though, is Mathilde's story, which fills in a lot of blanks in sometimes jaw-dropping ways. (Fans of Gone Girl and The Girl on the Train, this is why you'll love it.)
The genius of this book lies in the juxtaposition of the two voices, addressing issues of destiny, creative potential, and the nature & meaning of marriage. Not a light read, but beautifully & poetically written without sacrificing the authentic voices of the characters, and the complexity and cleverness offers enough relief from the darker nature of the story to make it brilliant.