Anti-Semitic myths of ritual murder are less developed and more belated in medieval Spain than in northern Europe, where they flourished since the twelfth century. This essay suggests one reason for this difference: the presence and increasing importance in late medieval Spain of the converso, a hybrid who blurs the boundaries between Christian and Jew. Using recent psychoanalytic criticism of the Prioress's Tale, Chaucer's sentimentalized representation of the murdered child's mother is contrasted with the very different one in Damián de Vegas's Memoria del Santo Niño de La Guardia (1544), an account of a 1489-90 alleged ritual murder that was instrumental in the Catholic Monarchs' decision to expel the Spanish Jews in 1492. Vegas characterizes the two mother figures in his tale as being deceitful, indifferent, and blind, all traits traditionally used to stigmatize Jews. This conflation of mother and Jew is a striking literary marker of the crisis of categories that contributed to the discrimination against conversos in medieval and early modern Spain.