G-Man Ted Riley (Lloyd Hughes ) is ordered to investigate happenings at Diamond Island, where a bogus Major Gray (Grant Withers) is reported engaged in manufacturing a new brand of secret gas for his own purposes. Riley blows up his motor boat just off the island and is picked up by Gray's men. On the island he discovers chemist Professor Baker (John Cowell) and his daughter, Anne (Marion Burns), are held captive by Major Gray.—Les Adams <[email protected]>