User: Can you summarize the book Annihilation?
Assistant: Annihilation is a science fiction book taking place in the southern US inside a mysterious Area X. A team is assembled to explore the domain of Area X, led by a character only known as the psychologist. The main character is known as the biologist. These expeditions are managed by a mysterious government organization known as the Southern Reach.

The expedition centers on two notable landmarks within Area X, the topological anomaly, which the biologists calls a tower but is really a tunnel, and a lighthouse. The expedition encounters an entity within the topological anomaly that "writes" living words of non-sense on the wall of the anomaly in fungus. 

Early in the expedition, the biologist is contaminated by the fungus of the words in the anomaly, which grants her immunity to hypnotic suggestion, which the psychologist uses to control the other members of the expedition. The plot follows the biologist pursuing the psychologist in search of answers, leading a confrontation at the lighthouse. The psychologist jumps from the lighthouse, presumably forced to by the entity behind Area X, but lives long enough to confront the biologist. During the climax of that encounter, the psychologist shouts "Annihilation!" multiple times, and it is revealed that this is a hypnotic trigger word designed to induce suicide in the other expedition members.

After the psychologist succumbs to her injuries at the base of the lighthouse, the biologist embarks on a journey north to an island that is possibly related to the disappearance of her husband, who was a member of the previous expedition.