The Dukalia Spy Ring
Lois and Clark are sent to report on the Dukalia-American Sports Festival. Anti-American sentiment seems high there, and Lois recognizes a disgraced former navy officer in attendance, Lang.
Investigating, they find that Lang has invented a new kind of air-sea submarine, and means to sell it to Dukalian consul Karl Wolff as revenge for the navy discharging him.
In a twist, however, it turns out that Lang has been undercover all along, using the submarine to draw out spies. Superman saves the day, as usual.