In his third of four action serials, horror star Bela Lugosi played Boroff, an internationally notorious fiend who's attempting to pawn off his deadly invention, a disintegrating gas, to the highest bidder. Before the gas can be manufactured, however, Boroff must go in search of certain hard to come by ingredients and the villain is thwarted at every step by US coastguard agent Terry Kent (Ralph Byrd and crusading newspaper woman Jean Norman (Maxine Doyle. In the serial's 12th and final chapter, "The Deadly Circle," Boroff is finally destroyed by his own invention, civilization thus saved for Democracy. Down on his luck by 1937, Lugosi could only watch as Republic Pictures' screenwriters Barry Shipman and Franklyn Adreon wickedly named his character "Boroff," an obvious reference to Lugosi-rival Boris Karloff. S. O. S. Coastguard nevertheless emerged as one of the Hungarian star's better vehicles, in no small measure due to its vigorous hero, Ralph Byrd, a handsome actor perhaps better remembered from Republic's Dick Tracy serials.