The Sleepy Lagoon Defense Committee originated as an ad hoc committee and evolved to a broad-based movement for legal justice on behalf of seventeen youth convicted of murder and assault charges in connection with the Sleepy Lagoon case in Los Angeles in January 1943. This essay chronicles the multidimensional organizing to shift public opinion in the case, in which activists skillfully utilized the specter of a fifth-column element made up of Mexican Sinarquistas and fascist sympathizers to achieve their goal. A diverse array of individuals and organizations, including those in the Mexican community as well as prominent writers and activists of other ethnic backgrounds, contributed to the successful effort to win public support and finance the appeal that ultimately overturned the convictions and won the release of the young men who were behind bars. (Contains 5 figures and 43 notes.)