A man claiming to be a historian from the future visits the Enterprise as it races to save Penthara IV from a nuclear winter.
An asteroid strike has thrown dust into the atmosphere of Penthara IV, and the Enterprise is on its way to keep the planet from freezing. A small time pod appears, and its occupant, Berlinghoff Rasmussen, says he is a historian from the twenty-sixth century who has come to observe the crew. Picard asks him for guidance on the risky plan to save the planet, but Rasmussen will not change history.
The crew grows suspicious as small items go missing. Rasmussen is in fact a twenty-second-century inventor who stole the pod from its real owner and has been collecting technology to take home. Data exposes him, and the pod returns to the future without him, leaving him in Federation custody.