The following version of the book was used to create this study guide: Michaelides, Alex. The Maidens. Macmillan Publishers, New York, NY, 2021. Kindle AZW file.

Mariana Andros grew up in Greece under the control of a cold but wealthy father. Her mother died when Mariana was an infant, and Mariana read all her mother's books from England. Mariana decided to attend Cambridge University. There, Mariana hoped to find love and friends, but she remained too shy to make those relationships happen until a chance encounter with handsome Sebastian. After dating throughout college, they married. When Mariana's only sister and brother-in-law died in a car wreck, they left a young daughter named Zoe. Mariana and Sebastian became Zoe's guardians, eventually settling her in as a student at Cambridge.

Mariana became wealthy upon the death of her father, who left her a vast estate. The only rocky point in her marriage was the lack of a child. On the advice of a doctor, Mariana and Sebastian took a trip to a vacation home she inherited in Greece, hoping the relaxed atmosphere would help them conceive. One morning, Sebastian went for a swim and drowned. His body washed up a few days later.

A year later, Mariana receives a frantic call from Zoe who says a body has been found on campus. She believes it is her friend Tara who confided in Zoe that Professor Edward Fosca threatened her just hours before she died. Mariana goes to Cambridge to be with Zoe who seems desperate to keep Mariana at her side. After Mariana realizes Zoe needs her, she decides to put her psychology skills to use. She meets a young student named Fred who takes an interest in her. Though Mariana admits to being drawn to him, she dismisses the possibility, partly out of her continued grief and partly because he is several years younger. Fred is undaunted, and Mariana finds herself confiding in him as she tries to find evidence to convict Edward.

Mariana discovers Edward has a group of young female students he calls the Maidens, based on Greek literature. Within days, three members of the group have been murdered. Mariana receives a postcard, just like the one she found for each of the other victims. When she finds a love letter to Zoe, she tries to believe that Zoe and Edward are involved in the murders together. In spite of her thoughts, she goes with Zoe to a remote area where the first was killed. It is then that Zoe reveals the horrible truth. She and Sebastian had been in a sexual relationship that began when Zoe was only 15-years-old. When Mariana's father found out, Sebastian killed him, making it look like natural causes. Sebastian and Zoe wanted Mariana's money for themselves, but Sebastian knew the husband is the first suspect when a wife dies. He and Zoe concocted an elaborate plan to kill several students at Cambridge, lure Mariana there, and then kill her. With the money Sebastian would inherit, he and Zoe could live luxurious lives. After Sebastian's death, Zoe decided to go through with the plan on her own. Mariana realizes the truth but cannot immediately face it. She allows Zoe to lure her to a remote location. Fred, operating on a premonition that Mariana is in danger, follows. Zoe stabs Fred, but Mariana hits Zoe who then falls on a knife.

Police arrest Zoe who survives. Fred also survives. When Mariana visits him in the hospital, she realizes that she is no longer adamantly against the attraction she has for him. As the novel comes to a close, Mariana agrees to visit Zoe in the mental facility where she is being held. She is not willing to forgive either Zoe or Sebastian, but she knows that talking to Zoe might help her own mental state. A colleague at the hospital asks her to wait, but Mariana goes to the end of the hall and opens a door.