In these lesson plans, students will act as CSI agents investigating the mysterious pathogen that caused the massive potato crop failure and resultant Great Famine of 1845 in Ireland. Through a variety of seven focused activities, students will map its diffusion, experience the history of the Great Famine, isolate and test samples using PCR and gel electrophoresis, create Wanted Posters of plant pathogens and take action in communicating their concerns of chemical controls of these pathogens and the danger of repeating history.