The military is performing a practice air raid on New York City. Sach convinces the boys that it is real and they go down to the recruiter's office and enlist. Meanwhile, Slip arrives at Louie's and finds out what just happened and goes down there to stop them. He is too late, as they have already joined, and is tricked into enlisting himself.
Louie tries to enlist as well, but is turned away as being too old. He was, however, in World War I and when he was there he invented the 'Hydrogen Ray', which did not work as intended. However, the army is using the plans for that ray as a decoy to try to capture spies that are at the local base…the same base the boys have been assigned to. The army decides to reinstate Louie to use him as bait for the spies. He ends up being kidnapped by the spies, and they try to get the secrets of the ray out of him. The boys come to his rescue and are rewarded with medals for bravery, and then sent to the brig for leaving their posts to rescue Louie.
