Karen is running along a beach in North Wales. She digs around in the sand dunes and finds an ancient bronze mirror, green with age. She tries to rub off some of the patina and finds herself in another era, nearly two thousand years earlier. As she cannot explain where she is from, they assume she ia a runaway slave and arrest her. In the course of the story, she goes to Rome, becomes part of a patrician household, witnesses the great fire of 65 AD, escapes and makes her way back to Britain - but not alone.