Condition Green: Tokyo was the warning posted almost daily at the gates of U.S. bases in Japan during May, 1960, when the US-Japan Security Treaty was revised and extended. Communist-led riots and demonstrations opposed to the treaty made it unsafe for Americans on the streets of Tokyo. Homes were burned, autos overturned, government offices ransacked. Americans were attacked, a leading politician assassinated, hundreds injured, and many killed. The revised treaty passed the Diet, but Leftist discontent forded the Prime Minister to resign.

U.S. Intelligence learns that Japanese Communists plan to seize control of the government on May Day 1970, but due to a rising tide of anti-American feelings and bloody anti-government rioting, is powerless to act. Only by dramatic and positive proof of a Red betrayal could the U.S. hope to turn the tide of popular sentiment against the Communists. Capt. Joe Holiday is sent on an 11th-hour reconnaissance flight over Communist China and Russia in hope of obtaining such proof—and obtain it he does. But to get the evidence into the proper hands, he must evade a swarm of Soviet fighters with his unarmed aircraft, and run a last deadly gauntlet of Soviet Surface-to-Air Missile sites.