The canopy keepers
(Book)

"Syrah Carthan doesn’t know why she accepted a job as the first female fire chief at Sequoia National Park, where, decades earlier, a forest fire killed her parents. That day, her brother, Romelo, disappeared, as if pulled into the scorched earth itself. Syrah has always had an uncanny affinity for the natural wonders of the park she protects, but after she sanctions a prescribed burn that goes terribly wrong, she quits her position in disgrace. However, when another devastating wildfire breaks out, Syrah, reluctantly pulled back into action, discovers an unknown world that has existed underground since the beginning of time. This secret society, built around the forest’s complex root system, is now divided into two factions. One is ruled by the Keeper, the giant sequoias’ benevolent caretaker. The other by a mysterious undoer, who’s determined to wage war on humanity. Through him, nature can retaliate and wipe out the earth’s careless ravagers for good. Torn between human loyalty and preserving the delicate balance of nature, Syrah must make a choice—one that will change both her destiny and that of the world above and below forever." --publisher's website.