When a tree cries out in pain, some unexpected heroes come to the rescue.       

Nema and her gang of young nematodes (tiny worms) embark on a dangerous journey underground. The Xenos, a group of wise but deadly bacteria, hitch a ride. The story of how they help the tree is full of action, life-or-death challenges and microscopic warfare. It is a story of co-operation and ancient partnership, about events happening all over the Earth, in the hidden worlds beneath our feet.