Stardate 45959.1. The Enterprise is recalled to Earth. Captain Picard investigates a macarbre artefact. A team of archeologists have discovered Lieutenant Commander Data's head, buried beneath San Francisco. The fact that it appears to have been there since the 19th century deepens the mystery. Trying to unravel this paradox in time, the crew of the starship Enterprise discover a community of time-travelling aliens, plundering Earth's past of neural energy stolen from dying humans.