Strange creatures resembling human skeletons attack "Bernie" Reinstein, a young woman who barely manages to reach Doc Savage's 86th floor headquarters and explain to the Man of Bronze and aides Monk and Ham that her father, a noted geneticist recently-escaped from Nazi Germany, has disappeared!
The trio and Bernie return to the site of her attack to discover one of the creatures lying on the ground, then trace his tracks to a nearby warehouse where they encounter a cloaked and slouch-hatted man leaving the building, who shoots Monk, whose "bullet-proof underwear saves him.
Later, while Monk analyzes tissue samples from the creatures, Ham takes fingerprint samples to Police Commissioner Weston, who's having dinner at the Cobalt Club with Lamont Cranston.
After Ham leaves, Cranston departs and becomes The Shadow, who learns of a possible tie-in between a case he's working on and Doc Savage's investigation, and, with Harry Vincent, heads to Lakehurst Naval Air Station in his autogyro.
Savage goes with Reinstein to her fiance, Paul's, apartment.
Leaving her in his armored car, Doc checks out the deserted and ransacked abode, discovering a clue pointing to the same location The Shadow is heading for.
Bernie sees Paul hiding in a nearby alley and goes to him, but is grabbed by a masked figure.
Doc returns, finds his vehicle empty and calls Monk and Ham, who are under attack by giant monster-men!
The Man of Bronze dashes back to his headquarters, but it's too late.
His aides are gone.
Doc heads to the air base in his own autogyro.
Meanwhile, The Shadow has discovered his destination...the zeppelin Hindenberg, and boards it!
Finding his target, a Nazi scientist, the cloaked hero is about to question him when a guard interrupts the interrogation.
The Shadow escapes into the superstructure of the airship, where a nervous Nazi guard, despite being told not to use his firearm, shoots at the hero, but hits one of the hydrogen-filled gasbags...
"What's going on in there" is you're about to discover that trapping Doc Savage and The Shadow and keeping them are two totally-different matters!
the thrilling climax of this serialized saga at