Message in the Sky — Sharon Dennis Wyeth

In the final book of Corey's Diary, Corey Birdsong and his family are living a full life in Canada, on their own farm, but they cannot forget about friends left behind, still in the grips of slavery.

In "Message in the Sky", Corey begins attending school, and his family, along with his friend, Mingo, are living well in Canada, where they've built their own farm. But, the Birdsongs cannot let go of the memories of their friends left behind in America. Corey and Mingo hatch a plan to help Aunt Queen, Mingo's adopted mother, escape, but Corey's parents forbid it, and start saving money to buy her freedom, instead. However, when Corey accidentally ends up on the American side of the Ohio River, he finds himself a conductor on the Underground Railroad!