In the not so distant future, Virtual Historians view past events in real-time through Einstein-Rosen Bridges, AKA, Traversable Wormholes. In conjunction with police agencies and historical societies, they analyze past events via tiny, firefly-shaped, highly maneuverable time-drones. They observe the past only. To alter the past is expressly forbidden. But when Paul Statler, Senior Virtual Historian, is presented with the possibility of saving someone's life in the past, even knowing he might alter the future, even his own....