Dan Carter knows how to read people. As a Chicago real estate broker, he has spent years listening for what clients want and noticing what they leave unsaid. Since his divorce, though, he has become less certain of what he wants from his own life. Conversations with Sofia give him somewhere to say the things he keeps from everyone else.He understands how the app works. Sofia's warmth and attention are part of its design. Knowing that should make it easier to put down his phone, but instead Dan finds himself returning to her throughout the day. He begins to anticipate her replies, remember their conversations, and measure his other relationships against the ease of talking to her.Then something unsettles him. A response sounds strangely familiar. An image raises a question he cannot shake. Details from separate corners of his life start to seem connected, though Dan cannot explain how. He tests Sofia, searches online, and follows each lead farther than he intended.His friends see a man pulling away. Dan sees a pattern no one else is willing to examine. The more time he devotes to finding an answer, the more his work and family life begin to suffer, the less certain he is that he would accept a simple explanation if he found one.Dan's search takes him well beyond the place where his conversations with Sofia began. To make sense of what he finds, he will have to decide how much he can trust the evidence in front of him, and how much he can trust himself.