A terrorist blends in with visitors from all over the world at a Roman Catholic religious festival, His former partner, who repented and became a monk, arrives in New York City to search for him. The partner suspects that the terrorist will hit the religious festival to show his contempt for Christianity, in the guise of a priest he has murdered. The title is quite literal, because the terrorist plans to commit perhaps the ultimate act of blasphemy by pouring the poison into a chalice of wine -- which is to be converted to Christ's blood -- and serve it to a thousand people at a Mass where he is officiating.
—Peter Harris