Babel 17

In the far future, after human civilization has spread through the galaxy, communications begin to arrive in an apparently alien language. They appear to threaten invasion, but in order to counter the threat, the messages must first be understood. During an interstellar war one side develops a language, Babel-17, that can be used as a weapon. Learning it turns one into an unwilling traitor as it alters perception and thought. This is discovered by the starship captain Rydra Wong. She is recruited to discover how the enemy are infiltrating and sabotaging strategic sites. BABEL-17 is the novel which catapulted Samuel R. Delany into the front rank of sf writers.