Arramar is a mindrider, an incorporeal being who lives in the minds of other species, and his people have arrived here to colonise the Earth. But Arramar begins to see that humanity is not an appropriate species for colonisation, not least because they are already inhabited by the indigenous, mind-dwelling monsters his people call "nightmares". Now, as a war between his colony and the nightmares begins to escalate, with collateral damage among the humans inevitable, he is desperately trying to persuade his people to leave. But the leader of the colony has disappeared and both his own people and the human military are hunting him down. His only allies in his struggle to save the Earth are a handful of humans whose minds he rides and who are as scared and confused as he is.