Escaped criminal Victor Murkland (Roy Barcroft) kidnaps the police commissioner and, with the aid of plastic surgery, takes his place.

Federal Agent Ted O'Hara (Clayton Moore) is called in to try to stop the wave of crime initiated by Murkland, not knowing that Murkland is posing as the police commissioner and is aware of O'Haras' every move.

The real commissioner is being held captive in a mental hospital run by Dr. Benson (Stanley Price).

Murkland's gang threatens to destroy a major tunnel being built underneath a channel, and blackmails the builder into paying him protection money.

[1] G-Men Never Forget was one of twenty-six Republic serials re-released as a film on television in 1966.