From the very first day an intelligence officer begins his training, he is primed on how to become the best salesperson in the world. Spies aren’t selling an ordinary product, however. The product they’re selling is treason. If an intelligence officer doesn’t close a deal, he might end up getting killed or spending the rest of his life inside a foreign prison. Treason, which is generally defined as betraying one’s country, is a pretty tough item to sell, particularly because the punishment for it is unforgiving. In the United States, when Ethel and Julius Rosenberg were convicted of conspiring to...