The story focuses on a young woman in late 20th Century Los Angeles who is dissatisfied with her hectic life, which includes balancing her career as a lawyer with being a mother and dealing with her deadbeat ex-husband and sexist coworkers. Believing the past was a better time, one evening, after a particularly distressing day, she makes a wish before a plaque of two Roman gods, Liber and Libera. The next morning, she finds herself waking up in the body of one of her ancient ancestors running a tavern in 2nd century Carnuntum, in what is now Austria.
In general, she finds out the hard way that life in the past was not quite what she thought it would be: slavery is taken for granted, there are no women's rights, no effective medicine or clean medical practices, little entertainment, and no tampons. Over the course of a year and a half, she is forced to revise many of her long-held modern prejudices, including those against alcohol and corporal punishment.
She survives epidemic disease (the Antonine Plague) and a Germanic invasion that is part of the Marcomannic Wars. She finds that early Christianity was uncomfortably zealous and apocalyptic; and, after a brutal rape by a Roman soldier, discusses the role of government and its duties to abused citizens with Roman Emperor Marcus Aurelius.
Eventually Liber and Libera fulfil her desire to return home. She wakes from a six-day 'coma' to discover that she can improve both her working and family life. Not only have her hardwon skills given her more empathy and self-confidence, but she now has great appreciation for the life that modern conveniences allow. With this new perspective she can much more easily and successfully deal with the stress and difficulties of her existence.
As is usual with Turtledove's novels, the attention to historical detail is excellent. Unlike the protagonist in Lest Darkness Fall the central character knows almost nothing about the history of the Roman Empire and has no mechanical skills. So, besides the disadvantage of being a woman in a small provincial city, she does not have the tools to change the course of events (her "inventions" are tries at onion rings and apple pies). Thus the authors focus on how one just survives in this strange environment, and the reader learns a great detail about a poor person's life in antiquity.