The Trap Door is the third book in the Infinity Ring series and was released on February 5, 2013. It was written by Lisa McMann, who is a New York Times bestseller of the Wake trilogy and Unwanted series.
Dak, Sera, and Riq return to the United States . . . and walk right into a deadly trap. The year is 1850, and the nation is divided over the issue of slavery. In these dark days, the Underground Railroad provides a light of hope, helping runaway slaves escape to freedom. But the Hystorians have taken control of the Underground Railroad from within. Now Dak and Sera are left wondering who to trust . . . while Riq risks everything to save the life of a young boy.