Mars is the new frontier: desolate, lawless and wild. Once home to an advanced alien civilisation, now home to every kind of riffraff from Earth hoping to build a new life amongst the ruins - or, better yet, plunder some ancient Martian treasure. The greatest treasure of all is the City of the Dead, the fabled tomb of the high kings and queens of ancient Mars. It promises riches beyond imagination; people will kill to find it. When Holly's archaeologist father is kidnapped by pirates who think he can lead them to the City, she sets out to rescue him. She teams up with a group of children who are, each in their own way, as lost as she is. Together they will follow a trail of clues that will lead them to the City of the Dead - and the not so dead Martians . . .