In 2009, a Palo Alto high school student died when he deliberately stepped in front of an oncoming train; within six months, the school lost five more students to suicide at those train tracks. A recent transplant to the community, Lee Daniel Kravetz's experience as a science journalist kicked in: what was causing this tragedy? More important, how was it possible that a suicide cluster could develop in a community of concerned, aware, hyper-vigilant adults? Exploring the concept of social contagion, Kravetz draws on research and insights from experts worldwide to unlock the mystery of how ideas spread and why they take hold, offering thoughts on our responsibility to one another as citizens of a connected world.