When investigative journalist Zara Okafor finds a forum thread listing 41 people who checked into a legendary, unmappable hotel on the Croatian coast and never came back, she does what no one else has dared: she goes. The Verlaine Hotel is real, exquisitely beautiful, and run by a mysterious woman named Mrs. Veil who already knows Zara's name before she arrives. What Zara discovers inside is not the horror story she expected — but something far more unsettling. The hotel is an experiment, begun by a stateless neuroscientist in 1947, that does something scientifically plausible and morally staggering to the people who stay long enough: it makes them think more clearly than they have ever thought in their lives. And then they choose not to leave. As Zara races to find the truth behind the 41 names — including a missing blogger whose last post said "Going in. Will report back" — she must confront the hardest question of all: what do we owe the people who choose to disappear, and what do they owe the ones left behind?