The sky went dark the morning of May 19, 1780, in New England. The darkness traveled quickly from the West and did not go away until the following day. At the time and in years following the event, many theories have been offered to explain the darkness. After receiving an overview of the situation, students working in groups form a hypothesis giving their explanation of the mysterious event. The students then receive three sets of clues, one set at a time, to help them solve the mystery.