When her brother is killed in the mysterious explosion of a new field-gun for the U. S. Army, Irene Eaton goes to Washington D. C. to call upon Colonel Shaw, head of the Army Military Intellegence. The gun explosion wa...展开s just one of many acts of sabotage recently pulled off by a foreign sabotage gang. Shw and his aides are the subject of increasing criticism from Congressmen and politicians such as Everett Brock because they haven't captured the gang members and leaders. Shaw appoints Irene to root them out and sends her off to the Dome Cafe which is the headquarters of the gang.
Irene Eaton offers herself to secret service chief Shaw for undercover work to find the saboteurs causing a rash of explosions, one of which killed her brother. She is accepted (despite having no experience), given a false identity and leads to a cafe, where she quickly learns who some of the underlings are and joins them. One appears to be James Huntley, a photographer she picks up under orders of the chief underling, after he swims ashore from an unknown vessel. However, getting the big boss of it all is the object, and after many red herrings he is revealed at the end of the movie, which culminates at the uppermost floor of the Washington Monument.