While listening to Walter's homemade shortwave radio, Harriet and Miss Brooks hear a weather warning of an impending hurricane. As acting principal, Connie shuts down the school and the gang takes refuge at the Conklin home.
The famous Hale Diamond has been stolen. Then, the wallet of Mr. Gates, with $10,000 in cash in it, is taken. Then a fortune in emeralds vanishes. Commissioner Weston concludes that the thief must be "The Shadow!" The Shadow battles the invisible killer who knows his secret identity.