Sally Scott carries a secret when she goes through WAVES training - a new kind of radio, the invention of an elderly man from her hometown. Against regulations, she takes the radio with her when she is posted on an aircraft carrier. Turns out, the radio picks up "secret frequencies", and allows Sally to detect the movements of enemy submarines. Sally 'fesses up to her commanding officers about the radio, and all is forgiven as Sally uses it to save the ship convoy, time after time. Sally's love interest, a pilot (whose Spartan mother, rather improbably, serves as a nurse on her son's aircraft carrier) is lost at sea during a mission and the convoy cannot turn back to search for him ... will he still be alive on the return trip?