Bloom (2020) is the first book in the Overthrow trilogy written by Kenneth Oppel, who has authored numerous bestselling books for young adult and middle grade audiences. This science fiction thriller features deadly plants that threaten to take over Earth as part of an alien invasion, and three teenagers who are mysteriously immune to the plants’ effects. Bloom won the 2021 Red Maple Award, was a 2022 Vermont Golden Dome Book Award Nominee, and won the 2022 Manitoba Young Readers’ Choice Award for the Sundogs category. As the story explores ideas of alienation and belonging, friendship and loyalty, Bloom’s protagonists discover what sacrifice and heroism mean in a time of crisis. Oppel is a well-known Canadian author within the young adult and middle grade genres, and his other series include the Silverwing series and the Airborn series. He has written one novel in the adult fiction category, The Devil’s Cure (2000).

This guide uses the e-book edition of the text published in 2020 by Knopf Books for Young Readers. Pagination may differ from print editions.

Content Warning: The novel depicts violence between humans and extraterrestrial plants, feelings of alienation, teenagers in foster care, physical alterations, and environmental tragedies resulting in deaths. It contains allusions to abuse, self-harm, colonialism, and serial rape by way of alien abductions resulting in pregnancy. The novel may indulge in problematic depictions of children in foster families.

Plot Summary

Anaya, Petra, and Seth are high schoolers on Salt Spring Island. Anaya and Petra used to be best friends, but that changed a few years prior to the novel. Around the same time, Anaya became allergic to just about everything. Now, she carries an inhaler and an EpiPen everywhere she goes, and her face is always inflamed; she also has excess amounts of mucus, as well as an acne condition. Petra developed her own allergy. If water touches her skin, she breaks out in an itchy and painful rash. Seth is living with Mr. and Mrs. Antos, his eighth foster family. He’s learned it isn’t worth the effort of getting close to anyone, so he keeps to himself. He definitely doesn’t show anyone the scars along his arms, which are from a childhood surgery to remove the feathers he was born with.

After an epic rain, black grasses begin growing at alarming rates all over the island. They ruin crops, emit toxic fumes, and ravage the entire population’s health. Soon, black vines are covering homes and strangling people in their sleep, while gigantic sacs, hidden underground and filled with acid, trap and feed on animals and humans alike. Anaya, Petra, and Seth discover they’re the only ones in their community who are immune to the effects of the invasive plants, which are suspected to be a form of bioterrorism. Anaya and Petra’s previous allergies improve, and all three notice their bodies are changing.

Dr. Stephanie Weber, a biochemist working for Canada’s Security Intelligence Service, wants to study the teens’ genome. If she can understand what makes them immune, she may be able to develop a vaccine against the plants’ deadly effects. She reveals the plants, which she calls cryptogens, aren’t from Earth. They’re part of an extraterrestrial invasion meant to colonize the planet. When she sequences Anaya, Petra, and Seth’s genomes, she learns they share half of their DNA with the cryptogenic plants. Dr. Weber believes their mothers had their memories altered after being abducted, raped, and impregnated by aliens. When the cryptogenic plants invaded, it triggered dormant sequences in their DNA. That’s why Seth’s feathers are growing back, Petra’s growing a tail and scaly skin, and Anaya’s growing fur and claws.

The trio doesn’t have much time to process their discovery before contact is made with Anaya’s dad, a botanist who specializes in fighting invasive plants and who disappeared when he flew to Cordova Island in search of a way to kill the cryptogenic plants. The video call with him cuts in and out but reveals Anaya’s dad is trapped and is in grave danger. Anaya and her friends convince the military to let them accompany the rescue team since they’re immune to the plants and Anaya knows the layout of Cordova’s eco-reserve.

Upon reaching Cordova Island by helicopter, they find cryptogenic plants have grown over the lake where Anaya’s dad is trapped, as if hiding him—and the soil he discovered that’s toxic to the plants—from view. Their helicopter crashes, killing the pilot and co-pilot and leaving the three teens, Dr. Weber, and two military operatives to fight off the plants and find Anaya’s dad. Before long, the aggressive and seemingly intelligent vines kill the two operatives. Anaya, Petra, and Seth use their new abilities to keep Dr. Weber safe and reach Anaya’s dad. From there, the teens carry out a risky plan to kill the giant pit plant from which all the vines are growing, allowing them to escape the island.

Over the next week, Anaya’s dad and Dr. Weber use the soil from Cordova Island to develop an herbicide they hope will kill the cryptogenic plants. As everyone waits in suspense to see if it works, Anaya, Petra, and Seth learn there are other teenagers being discovered around the world who are just like them. The trio, along with the rest of the world, celebrates when the plants begin to die. As they watch, though, it begins to rain. Droplets that look like tiny eggs settle on the ground. Then they begin to hatch.