George Peppard, Mary Tyler Moore, Dom DeLuise, John McMartin, Nathaniel Frey, Charles Lane, Jeanne Arnold, George Furth, Morty Gunty, Joe Ponazecki, Frank Campanella, Susan Saint James, Don Stroud, Nat Polen, Thelma Ritter
A new infection that simply makes people feel happy is treated as a threat by the authorities while its "victims" work to spread it to others.