Psychologist Tara Sheridan is an oracle who once used her gifts to profile criminals. When one criminal left her scarred body and soul, she gave up profiling. Born into a secret cult of women magic users and oracles called Delphi's Daughters, she walked away from them years ago.

When her mother's old friend Sophia asks for help finding a missing scientist, Tara agrees reluctantly. Lowell Magnusson was working on dark matter for the military, and what he discovered could be very dangerous to everyone. The military are anxious to keep his work a secret, which makes Tara's job even harder.

FBI Agent Harry Li has also been assigned to the missing scientist case. A solid man, he neither believes in magic nor has any patience with military stonewalling. When Tara starts to develop feelings for him, she fears that her abilities and her past will disgust him. Their romance starts somewhat abruptly, minus much of the flirtation or bickering typical of urban fantasy couples.

The powers of the Pythia, the leader of Delphi's Daughters, are weakening. Even though Tara has abandoned the secret society, many of its members are convinced that the Pythia will choose Tara as her successor. Adrienne, another powerful oracle, will let nothing stop her from become the next leader – even killing Tara.

Tara's oracle magic manifests through Tarot cards inherited from her mother. When she has a problem, she says her question out loud and then reads the cards. Each of the cards are described in detail as well as Tara's feelings and intuitions about them. The deck stays always the same, so it is possible that the intuitions she gets from the cards are limited. She writes down her thoughts intending to think about them later, but she never has the chance because the plot moves quickly forward. While initially her use of magic is rusty after abandoning her profession and the world, she picks it up again quickly.

The secondary characters are quirkier than Tara and Harry. Tara resents Sophia because although Sophia knew that Tara's mother was dying, she didn't say anything to Tara. The other oracles possess flashier powers: the Pythia controls fire and sees the future in the flames, while Adrienne has some control over earth and sees portents by casting runes. The Pythia, an old Arabic woman accustomed to commanding her circle of women, nonetheless knows that even when she can see the future, she cannot always change it. Magnusson's daughter - with whom Tara quickly bonds - is studying to become a scientist and is frightened for her father. Harry's adoptive father is a wily old man who lives in a forest.

Even though Tara is the main point-of-view character, some events are seen from other people's point-of-views, including Harry, Adrienne and the other enemies.

Tara can hold her own in a fight and has a dark past that forces her to keep everyone else at an arm's length, yet she opens up to a possibility of a romance. Since her magic actually depends on her being open to the world, she also possesses a softer, more intuitive side, which sets her apart somewhat from typical urban fantasy heroines.