The stories of nine people—Nicholas Hoel, Olivia Vandergriff, Ray Brinkman, Dorothy Cazaly, Neelay Mehta, Patricia Westerford, Douglas Pavlicek, Mimi Ma, and Adam Appich—are woven together not just with each others', but with those of the trees that they come to see as crucial conduits to the longevity, health, and sustainability of the entire planet. The grave danger that the rapacious and capricious cutting down of trees presents is the main catalyst for action for most of these characters, while others engage with the natural world in more peripheral, albeit still profound, ways.
Nicholas Hoel is a restless, struggling artist living on the Hoel farm, which was started by his ancestor centuries ago. His insurance money is gone and he is preparing to vacate the premises, unsure of where to go next. This is when fate—or, the machinations of the trees themselves, which at times seem to communicate with the characters—brings him into contact with Olivia Vandergriff.
Olivia is a cynical college student who loves to party when she is accidentally electrocuted by touching a light socket with her wet hand while high. While she is lingering between death and life, she feels presences calling to her. When she awakes, she feels changed, and is soon compelled to leave her school and her life and follow the voices westward. It becomes clear that the trees are encouraging her to go to California to help save the remaining 3% of the giant redwoods, a vision which solidifies and deepens over time. Nick, entranced by her charisma and her certainty, hitches his fate to hers.
Mimi Ma is an engineer who, while smart and attractive, struggles to find her place in the world. She desperately misses her father, a brilliant Chinese immigrant and fellow engineer who committed suicide when she was young. She is drawn to the trees outside her Portland office window, and begins to anguish over their imminent destruction. After they are cut down one day, she mourns their loss and meets Douglas Pavlicek, a Vietnam War vet who had been wandering the country, also looking for meaning. In his travels Douglas had discovered the grotesque deforestation occurring and decided to plant seedlings as a response, but was traumatized to learn that big logging companies only profited from those plantings. As a result, he is looking for a way to get involved and protest this ravaging of the trees.
Adam Appich, an awkward child and angry teenager, experiences an intellectual epiphany when he comes across a book that explains how humans are hobbled by their cognitive biases, safeguards leftover from earlier stages of evolution. He pursues degrees in psychology and enters a grad program where he decides to focus his dissertation on the group mentality behind environmental protestors. He heads west to interview them and collect data.
Ray and Dorothy are a married couple; he is an intellectual property lawyer and she is a stenographer. Their relationship is tempestuous for a while, as Dorothy does not want to be “owned” by anyone, but they eventually marry. She is distressed that they cannot have a child, so the two of them find other ways to create meaning in their lives—reading, hobbies, acting. While Ray is happy and content with their life, Dorothy is increasingly restless.
Patricia Westerford has been fascinated by the communicative abilities of trees ever since childhood, a time in which she would travel around the country with her father and listen to him talk about those species that most people take for granted. After going to college for forestry, she enters graduate school. She excels there and becomes a lecturer. She publishes an article on something groundbreaking and relatively controversial—trees as social beings. The paper is received well at first, but a cadre of more established academicians lambast it, and her reputation falters. Bereft of everything that has meaning to her, she almost commits suicide. After deciding to live, she travels into the mountains and communes with the trees there and marvels at the old growth forests. She gets a job for the Bureau of Land Management, taking care of an area and engaging with visitors. She prefers this solitary life.
Neelay Mehta is the son of two Indian immigrants living near Palo Alto. As a young man he builds computers with his father and becomes a skilled coder. In his youth he falls out of a tree and becomes paralyzed from the waist down. This does not deter him from pursuing his desire to code, and he graduates from Stanford and eventually founds his own company, Sempervirens. His famous game is Mastery, in which players enter this universe and travel, build, conquer, etc. It goes through numerous editions, each one more and more realistic and absorbing.
Nick and Olivia join a group of nonviolent radicals in California and give themselves "tree" names, Nick becoming Watchman and Olivia becoming Maidenhair. When they are asked to tree sit in a giant redwood called Mimas for two weeks, Olivia leaps at the chance. Their stay ends up lasting for more than a year, during which they watch as the forest around them is decimated. They are eventually joined by Adam Appich, who is there for his dissertation. He ends up identifying with Nick and Olivia, and recognizing the validity and nobility of their fight. The night he is there, they are finally forced out of the tree and arrested so Mimas can be cut down. Nick and Olivia decide to do more work in Oregon while Adam heads back to academia.
Mimi Ma and Douglas go to protests, where they are brutalized by the police and arrested several times. Mimi is eventually fired from her job and, like Douglas, becomes a full-time activist.
Changed by his time with Olivia and Nick, Adam goes to Oregon to rejoin them, and meets Mimi Ma, now going by the name Mulberry, and Douglas, going by Doug-fir. They are now part of the same activist camp. The “Cascadians,” as they call themselves, believe that they are finally achieving something until their camp is destroyed by the forest authorities and law enforcement. In the altercation Mimi and Douglas are both badly injured.
In retaliation the group sets fire to logging equipment. Pleased by the results, they set two more fires intending the third to be their final act. During the final act of arson Olivia is injured and dies, and the four remaining activists burn her body and scatter. The fire is deemed the work of a crazed killer and the logging continues. Mimi Ma sells a priceless heirloom her father passed down, which ensures that she can reinvent herself. Nick becomes a vagrant, utterly bereft by his loss of Olivia. Douglas becomes a BLM ranger, and Adam returns to academia again.
Douglas is still haunted by what happened and writes down everything in his journal using everyone's forest names. Nevertheless, his journal is discovered and the FBI arrests him. In order to protect Mimi Ma, he decides to give up one name and goes to New York City where he encounters Adam. They reminisce about the past and the fire, and though Adam doesn't know what Douglas is doing, he says enough to be later arrested.
Adam is sentenced to 140 years in prison, which strikes him as a small price to pay as it is barely any time in tree life. Douglas’s deal nets him seven years and an eligibility for parole in two.
Mimi Ma, who is now living and working in San Francisco as an unconventional unlicensed therapist of sorts, hears about the arrests and realizes that Douglas turned in Adam to protect her.
Ray suffers a devastating brain incident and is a veritable vegetable. This is right after Dorothy told him she was leaving him, but she ends up staying with him for the rest of his life. The two achieve a more intimate and meaningful relationship than ever, and find relief in learning about the trees around them. Ray dies and Dorothy lovingly promises she will be with him soon.
Patricia writes a second book and starts a seed bank, which garners her more and more fame and publicity. She is always uncomfortable in crowds but is pleased with her work. After Dennis passes away, she mourns deeply and wonders about her work. She is invited to a conference of the best and the brightest in the worlds of science, technology, and the arts in order to give them hope about trees’ ability to make a better future for people, but she knows she cannot give the attendees a false salve. She decides to be honest and carry out the only act that a human can do to really help the planet—commit suicide. After the end of her stirring talk where she speaks of the magnificence and importance of the trees, she sips poisonous extract from a tree and collapses on the stage.
Neelay knows that Mastery is not enough, and, galvanized by his engagement with the trees on Stanford’s campus and his witness of Patricia’s suicide, decides to pursue a new type of game—a game where players are essentially figuring out how to “unsuicide” their planet, how to live sustainably.
Living in the forest, Nick creates a giant message from branches and dead logs that can be read from space. He is helped in this project by a Native American man who happens to be passing by, and later by some of the Native American's family. The message, which reads "Still," will be legible from space for 200 years before it is absorbed into the forest.