A young woman named Mae Holland arrives at the campus of a company called the Circle, one of the most highly praised and innovative tech companies in the world. Mae has been recruited to work at the company, thanks to the help of her close friend and college roommate, Annie Allerton, who is one of the Circle’s highest-ranking employees. Annie welcomes Mae warmly and gives her a tour of the facilities, which are beautiful and cutting-edge. Everyone Mae meets is extremely gracious and enthusiastic about Mae joining the company.
During the course of the tour, Annie tells Mae about the Circle. It’s run by three people who are known as the Three Wise Men. Ty Gospodinov, the founder and most tech-savvy of the Wise Men, is a recluse and he almost never appears in public anymore. Tom Stenton, the most aggressive and money-hungry of the Wise Men, is in charge of the company’s “dirty work.” Finally, Eamon Bailey, the most charismatic and beloved of the Wise Men, is responsible for realizing the company’s vision of global interconnectedness.
Mae begins working for the Circle in the Customer Experience department. There, she spends her time interacting with customers who have questions about Circle products. Her job seems to be generally superficial and it’s not clear how it fits in with the company’s mission overall. Mae quickly finds that the Circle throws parties and social events near-constantly. At one party, she meets a quirky employee named Francis Garaventa. Mae quickly learns that Francis is an orphan, and several of his siblings were kidnapped and killed when he was a small child. As a result, Francis is working on a project for the Circle designed to track abducted children. Mae also attends presentations led by Eamon Bailey. At one, Eamon introduces a program called SeeChange—a system of cameras that allow Circle users to watch any point on Earth at any time.
Although Mae is impressed with the utopian spirit of the Circle, she doesn't spend as much time on campus as her coworkers do because she likes to visit her parents. Her father is suffering from MS and he needs constant care; unfortunately, his healthcare doesn’t provide him with the painkillers that he needs to feel comfortable. At work, Mae is encouraged to spend much more time participating in social life at the Circle. She is supposed to attend parties and gatherings, and, much more importantly, she is urged to post online about her activity. Sensing that this is important to her job, Mae throws herself into the task of building an online presence: she stays up late at night posting statuses, liking other people’s videos, etc.
Around the same time, Mae meets a mysterious man named Kalden. Kalden asks Mae questions about herself and about her work, but he refuses to answer many questions about his own life—he doesn’t even give Mae his last name. Mae tries to find Kalden online, but she can’t find anyone with his name. Later, Mae goes on a date with Francis, and they kiss.
The day after their date, Francis helps give a presentation about a new dating website called LuvLuv; during the presentation, he demonstrates the website by displaying Mae’s personal information. Mae is furious with Francis and she refuses to talk to him. Soon afterwards, she learns that her father’s health is declining rapidly. She goes home to visit her father, and, during her visit, she argues with her old boyfriend, Mercer Madeiros. Mercer expresses his skepticism about Mae’s new employer and he suggests that constant texting and social networking are destroying Mae’s relationships with her friends and family. Around the same time, Mae meets Kalden at a Circle party, and they have sex in a secret room.
At work, Mae learns that she can put her parents on her company’s health insurance plan; with Annie’s help, she does so. Meanwhile, the Circle begins to push the idea of becoming totally transparent (requiring its users to share all their personal information and experiences with other users). The Circle installs cameras almost everywhere on its campus. In secret, Kalden and Mae meet up in the bathroom (one of the only places without cameras) and have sex.
One night after seeing Mercer and her parents for dinner, Mae goes out to the beach and sees an unreturned kayak near her favorite kayak shop. She decides to take it out and then return it, planning to leave it just as she found it. When she returns to land, however, she’s surprised to find police officers waiting to arrest her. Mae is forced to call the owner of the kayak store, a woman named Marion. Although she’s ultimately not arrested, the experience frightens Mae. The next day, Mae learns that Circle users reported Mae after they saw her “stealing” the kayak on a hidden camera installed near the beach. Mae goes to meet with Eamon Bailey, who persuades her that “secrets are lies” and that human beings have a moral obligation to share their experiences with other people. Afterwards, Mae posts online near-constantly, sharing every detail of her life with other people.
The novel jumps forward almost a year. The Circle has grown to handle virtually all of the world’s information flow, and Mae has gone transparent and has been promoted to being a virtual tour guide for the company. As part of being transparent (which is inextricably linked to her job as a guide), Mae wears a lens around her chest at all times that allows anyone in the world to see what she sees and hear her voice. Mae savors her transparency, noting that it keeps her honest and energetic at all times: she always has to be “on” for her millions of watchers. Mae revives her relationship with Francis, but is unable to have sex with him, since he suffers from premature ejaculation. Mae also finds herself growing increasingly distant from Annie, who seems overworked and envious of Mae’s burgeoning popularity at the company and with its users.
Mae learns that her family has been “disrespecting the Circle.” After her parents accepted the company’s health insurance, the Circle installed cameras in their home, which Mae’s parents then covered with cloth to block their view. Furious, Mae begs her parents to uncover the cameras. Mercer tells Mae that her parents deserve privacy—a suggestion that Mae dismisses as absurd.
At work, Mae proposes a new idea: to require all Circle users to vote online through an interface controlled by the Circle. Eamon Bailey and Tom Stenton like this idea, and they further propose that the company require all Circle users to pay their taxes through the Circle, test their children through the Circle, etc. The resulting program, called “Demoxie” allows anyone in the world to vote on any topic. Mae gets several phone calls from Kalden, in which he urges Mae to speak out against the Circle because it is becoming dangerous and totalitarian. Mae ignores Kalden. She stays up late at night posting online, and she becomes paranoid and anxious about the smallest problems.
The Circle proposes projects that would allow police officers to target people who might become criminals, though they have not yet committed any crimes. Meanwhile, Mae realizes that Annie is suffering from crippling anxiety. Annie has signed up as a guinea pig for a new Circle program that tracks people’s ancestry and family history. Through this program, Annie has discovered that some of her ancestors were slave owners, and as a result, her online followers are sending her cruel messages. Mae tries to help Annie by telling her own watchers—millions of them—to be supportive of Annie and overlook her family’s crimes.
Mae gets a letter from Mercer explaining that he’s going to become a hermit in order to escape the surveillance of the Circle. Shortly afterwards, Mae demonstrates a new Circle program that is designed to track down fugitives. She chooses to demonstrate the program on Mercer, and she sends a team of drones flying after him. In the middle of her demonstration, Mercer drives his car into a gorge in order to escape the drones (and, perhaps, to escape the surveillance culture that the Circle has enshrined more generally). He dies—it’s an apparent suicide. Mae is distraught, but Eamon Bailey convinces her that Mercer was a disturbed young man and that she played no role in his death.
Mae is finally introduced to Ty Gospodinov, the third and most reclusive of the Wise Men. She’s amazed to see that Ty is actually Kalden. In private, Ty explains that he’s been trying to destroy his own company for years: he never wanted the Circle to destroy peoples’ privacy, and believes that Tom Stenton is going to turn the Circle into a tyrannical monopoly. He begs Mae to use her influence to denounce the company.
In the brief, final part of the novel, Mae has chosen not to denounce the company, but rather to inform Eamon Bailey and Tom Stenton of Ty’s subversive plans. Stenton and Bailey then placed Ty under arrest (or potentially murdered him), and Mae hasn’t seen Ty since. Mae visits Annie, who had a nervous breakdown following her participation in the genealogy project and is now in a coma. She looks at the screens showing Annie’s brain waves, and resolves to propose a project for listening to other people’s thoughts. The novel concludes, “The world deserved nothing less and would not wait.”