The Trap Door by LISA McMANN

History is broken and three children must travel back in time to set it right. Dak, Sera and Riq turn their attention to the next of the Great Breaks - and this one turns out deeply personal for Riq. In the years leading to the US Civil War, the Underground Railroad was integral to saving the lives of runaway slaves and spreading the gospel of abolition. But the SQ doesn't want slavery to fail. They've planted their agents all along the trail to freedom - and it's up to Dak, Sera, Riq and a former slave called Harriet Tubman to root out the bad guys.