Heretics of Dune

The wheel of history has turned full circle: the deserts have returned to Dune and with them the giant sand-worms. The death of the Tyrant Leto II triggered the release of a swarm of sand-trout, the earliest stage in the sand-worm cycle. They and their descendants have reversed the ecological miracle which changed Rakis (as Dune is know known) from a burning desert to a verdant, pleasant world.  Book 5 of series.