Sheldrake opens the book by describing a day in the rainforest during his ecological field work. His primary focus is a large tree, but the forest around him teems with life of all kinds. Many kinds of plants sprout from the tree’s roots, while others grow entangled with its canopy. Howler monkeys and toucans scream in the treetops, while snakes, tarantulas, and millipedes hide in the thick understory. Sheldrake has one goal: to follow a single tree root through the chaos as far as he can go.

It is slow work; after an hour he is soaked, is covered in mud, and has only moved a meter. He has learned to identify different trees by smell, so he pokes his nose into the trench he has dug, searching for a specific strong scent. As he follows the root, it becomes smaller and smaller and divides into countless branches. The branches, in turn, are covered in their own networks of minuscule fungal filaments. Sheldrake hopes to study the relationships between fungi and trees, so he has finally found what he is looking for.