The series follows the Murrys - a family that are frequently thrust into adventures that span multiple planets, dimensions, and eras.
In this story, Meg's daughter Polly is staying with her grandparents in New England when their neighbor retired Bishop Colubra discovers a "time gate" - a doorway to three thousand years in the past. Polly and friends find themselves trapped in the past, caught between two Native American tribes at war.
As in so many of her books, L'Engle spices the story with religious references and philosophies. She never overwhelms the reader with preaching or dogma; rather, she raises questions and shows different relationships between men and God. Some worship a single creator, while others see gods in their ancestors or in each force of nature; some believe in a loving, parental God, while others fear a vindictive god, who demands blood sacrifices. Unlike stories in the Old Testament, the snake featured in this story is a force for good. I found it interesting that the Christian Bishop was accepting of the beliefs of druids. They had fundamental theological differences, but they chose to focus on their common beliefs.
There are a few weaknesses. The skepticism of Polly's grandparents is inconsistent with their previous encounters with time and space travel; and conflicts are resolved a little too conveniently at the end. Coincidences occur that border on a well-timed miracle. It stretches belief, but that is probably ok in a book about time travel.
An Acceptable Time is a story of selfishness and betrayal. But it is also about forgiveness and redemption and the different aspects of love. It is a story of hope and a fitting end to this series.