Underground is an average Warner Bros. suspenser, given a boost by its unrelenting portrayal of Nazis as verminous scum--several months before America's entry into World War II. Jeffrey Lynn plays an impressionable young European who is intoxicated by the "glories" of National Socialism. Lynn's brother, Philip Dorn, is on the opposite side of the fence as an announcer for an underground Resistance radio station. At first scornful of his brother's activities, Lynn soon learns that Hitler isn't the saint he believed him to be--especially after several of his friends are liquidated by the Gestapo. Lynn belatedly joins his brother's cause and, at the cost of his own life, helps the Resistance thwart a band of fifth columnists. Underground is a solid piece of film craftsmanship, lacking only the big star names that would have made it a box-office hit.
by Hal Erickson synopsis