Charles Spark is an expert on body language, a bestselling author and a consultant (or walking lie detector) much in demand with industry and government. So when the aliens arrive, who better to join the team that will attempt to understand them?But even though these insectoid aliens - the "Flies" - in their pyramid-ship speak both English and Russian, they seem unreadable. "We have come to your planet to remember it," they say and at first they seem indeed to be a bizarre group of intergalactic tourists.When human beings start to interfere, things begin disappearing. The Dome of St Peter's in Rome is the first to go, followed by downtown Prague, old Mombasa, Münich, the heart of New Orleans.In an effort to understand what has happened, Spark, and a strange group of pilgrims, embark on a bizarre journey to Mars - where the city of Münich has reappeared in a canyon. And where time, and memory, have become manifest.