The Parallelogram Affair was an incident of espionage in the early 23rd century that involved all four great interstellar powers of the time: the United Federation of Planets, the Romulan Star Empire, the Klingon Empire, and the Orion Colonies.
In reference stardate 1/6908 (c. 2233), Orion authorities discovered a spy ring in which a guldin of Grey Orions received sensitive Klingon and Orion information, and relayed it to both the Federation and Romulans. They interrogated the Greys, but executed them after they refused to talk.
A young couple from the Federation were declared suspects in the spy ring and were arrested by the Orions as they left the Rigel system. They disappeared, and were not seen again.