A cursed book sends a young woman on a philosophical journey through an alternate dimension in this "stylish and dizzying" novel by the author of PopCo (The New York Times). Graduate student Ariel Manto has a fascination with nineteenth-century scientists-especially Thomas Lumas, the mysterious author of The End of Mr. Y, a book no one alive has read. When she uncovers a copy at a used bookstore, Ariel goes down an interdimensional rabbit hole of science and faith, consciousness and death, space and time, and everything in between. And to make matters worse, the CIA is onto her. Following in Mr. Y's footsteps, Ariel swallows a tincture, stares into a black dot, and is transported into the Troposphere: a wonderland where she can travel through time and space using the thoughts of others. There she begins to understand all the mysteries surrounding the book, herself, and the universe. Or is it all just a hallucination?