By pure chance, scientists detect a signal from space that may be communication from rational beings. How can people of Earth understand this message, knowing nothing about the senders--including whether or not they even exist?

Written as the memoir of a mathematician who participates in the government project (code name: His Master's Voice) attempting to decode what seems to be a message from outer space, this classic novel shows scientists grappling with fundamental questions about the nature of reality, the confines of knowledge, the limitations of the human mind, and the ethics of military-sponsored scientific research.