The team investigates an astronomical detective story. In October 2017, astronomers spotted the first ever object to visit our solar system from outer space. They called it 'Oumuamua. Its discovery set off a hurricane of press speculation and a major scientific investigation. The Sky at Night goes to Queen's University in Belfast, which has become the centre of scientific research on this cosmic visitor. When they first spotted it, all scientists knew was that it was small, it was travelling fast, and it came from outside our solar system. What did it look like? How had it formed? What was it made of? Where had it come from? To answer these questions, the team pieces together all the clues that scientists have extracted from the small amounts of data collected as 'Oumuamua flashed through the solar system.