The novel “The Ragged Astronauts” by Bob Shaw was published for the first time in 1986. It’s the first book of the trilogy of the Land and Overland trilogy. It won the BSFA Award for best science fiction novel of the year.

On Land the situation has been stable for a long time but suddenly the ptertha, creatures potentially lethal because of a poison, become an even greater threat. Their poison seems to have become even deadlier and start to actively attack people.

Among the castes of one of Land’s kingdoms’ feudal society, it’s the philosophers who study the ptertha to seek a solution to the problem. Their old leader has a revolutionary idea: migrate to Overland, Land’s twin planet divided from it by a few thousand kilometers. Airships can make the trip but only when the situation begins to be desperate the King decides to implement it.