"A Mighty Big Imagining" tells the story of ten-year-old Rachel, who in 1783 arrives in northern Nova Scotia with her mother, where they reunite with Rachel's stepfather after escaping slavery in South Carolina. Like many slaves during the American Revolution, Rachel's family aided the British war effort, in return for which they were promised their freedom as well as title to land in the British Colony.

Their joy at gaining freedom in a safe new home is dashed when they arrive, for the land they are given is barren, the weather frightful. Worse still, Rachel's mother is pregnant. For a while, Rachel even believes they were better off as slaves - at least they were warm and didn't go hungry.

Despite the adverse conditions of their new life, Rachel is determined not just to survive, but to make the most of her freedom. She wants to learn to read and write, and to help her family turn their squalid hovel into a home. With perseverance, pluck, and the help of a native girl named Marie-Andree, she will help herself and her family to survive their first winter of freedom."