In 2016, Matthew Gavin Frank travelled along South Africa's notorious Diamond Coast to report on the illicit trade that supplies a global market. Immediately, he became intrigued by the ingenious methods used in facilitating this trade—particularly, the illegal act of sneaking carrier pigeons onto mine property, affixing diamonds to their feet, and sending them into the air. Investigating a long overlooked true-crime story dating back to the founding of the De Beers Corporation, Frank weaves interviews with local diamond divers who raise pigeons in secret with harrowing anecdotes from former heads of security, environmental mangers, and vigilante pigeon hunters, revealing how these feathered bandits became outlaws in every mining town.