The secret referred so in the title does not remain one for very long, at least for the reader. However, I would be tempted to think that it is revealed much later for the author, if Hoffman did not so heavy-handedly make references to through out the first 60 or so pages.
Not that the story gets better after the cat and mouse game, where any cat worth its fur would have caught the mouse in the very beginning, when the truth is revealed and the story moves on. Instead the reader gets to endure the endlessly self-reflecting journey of Iris, a young woman who, well, more or less is searching for herself throughout the novel.
The premise of the novel is actually fairly interesting, but the execution leaves much for desire. First, while the idea is based on scientific developments, the discussion of the topic is a fairy tale with no deep thought or research into the matter: instead, we get fearful images not based on anything rational or though-out, in a style that fails to affect you.
Second, for a story discussing the emotional journey of a single person and filled with self-reflection, the writing feels disconnected from its characters. Not only did I have problem believing in the narration (for example, remembering exact things from the memories of childhood without any sense of unrealiability), but also with the feelings of the character. Iris's reactions are either disaffected or overt, ranging from numbness to "the worst teenager ever" rages without emotionally logical background.
Thirdly, this disaffection is perhaps related to the fact that the author seems to be more interested in her own writing than in the novel. The language often reaches for heights, trying to evoke poetic musings and move in dramatic shifts, where it should be concentrating on Iris. What is worse, it fails in its attempts and does not even reach the comical, but stays just plainly on the level of irritating.
Overall, the book is an ambitious attempt, but sadly blows any potential it might have had.