Two newly-appointed postal inspectors, Frank Marshall and 'Slim" Hewitt, set out to track down the sender of a time-bomb to a U. S. Senator and, during their investigation, run across a hooded organization that is terrorizing an American city. They also meet Don Foster, who is loud in his condemnation of the terrorists, and his sister, Nancy, who fears for her brother's life.
| Actor | Role |
|---|---|
 Bruce CabotFrank Marshall | Frank Marshall |
 Marguerite ChurchillNancy Foster | Nancy Foster |
 Crawford WeaverSlim Hewitt | Slim Hewitt |
 Ward BondDon Foster | Don Foster |
 Charles Cahill WilsonColonel McCollum (as Charles Wilson) | Colonel McCollum (as Charles Wilson) |
 John HamiltonCummings | Cummings |
 Arthur LoftGardner | Gardner |
| NNick CopelandLefty (as Nicholas Copeland) | Lefty (as Nicholas Copeland) |
 John TyrrellFeeney (as John Tyrell) | Feeney (as John Tyrell) |