Janet Smith gave a great plenary address at this years UFL Conference on the question of whether it is morally permissible to lie to abortion clinic workers to obtain the truth about their practices. She notes at the outset that both St. Thomas and St. Augustine believed that all lies are immoral, but in some circumstances are venial sins. She questions these conclusions, asking whether these saints have adequately taken into account the fallen nature of this world. For a good introduction to the debate over lying to get the truth about abortion clinics, look at her First Things essay, Why Tollefsen and Pruss are Wrong about Lying.