Four people with radically different outlooks on the world meet on a train and start talking about what they believe. Their conversation varies from cool logical reasoning to heated personal confrontation. Each starts off convinced that he or she is right, but then doubts creep in.

In a tradition going back to Plato, Timothy Williamson uses a fictional conversation to explore questions about truth and falsity, and knowledge and belief. Is truth always relative to a point of view? Is every opinion fallible? Such ideas have been used to combat dogmatism and intolerance, but are they compatible with taking each opposing point of view seriously? This book presupposes no prior acquaintance with philosophy, and introduces its concerns in an accessible and light-hearted way. Is one point of view really right and the other really wrong? That is for the reader to decide.