Though Captain Midnight has been given up for lost, his three chief agents, Chuck Ramsay, Joyce Ryan and Ichabod Mudd, now co-Commanders of the Secret Squadron, are carrying on the battle against Ivan Shark and his race of slaves. Arriving by plane, they went straight to the chief of police and obtained the map describing the location of the valley of the lost people. Meanwhile however, Shark himself had landed at the ranch outside of town, and having learned from Pedro da Silva that the map was in the hands of the Secret Squadron agents he brutally killed the Braziilian and then devised a diabolical scheme for regaining possession of it.