Heartfire

Alvin marries Peggy, and they conceive a daughter (not born by the end of the book).
Alvin, Verily Cooper, Arthur Stuart, and Mike Fink are joined by John James Audubon, a French-speaking painter of birds. This group go to a Puritan-dominated place near Boston and end up confronting the witch laws.
Meanwhile, Peggy has gone to the Crown Colonies - slave states that ruled by the Stuart dynasty in exile - in an attempt to free the slaves.
We learn the story of Purity, a Puritan girl whose parents were hanged for their knacks, which are considered witchcraft by the Puritans. Purity meets Alvin's band and Arthur Stuart tells her the whole story of their travels. Purity goes away convinced they are witches and tells a local witcher, Quill, who is evil and twists her words against her and the boys. Quill intends to hang them as well as Purity.
Alvin whisks away Arthur Stuart, Mike Fink, and Audubon by leading them into the greensong that lets them run hundreds of miles without tiring, but turning back without the others en route. Alvin gives himself up to the men sent to bring in the "witches" while Verily hides for the moment.
Quill has both Purity and Alvin running in tight circles to wear them down - a semi-legal form of torture, intended to make them confess to witchery. Verily comes by and loudly scolds Quill in front of the crowd, saying it's inhumane.
At the trial, Verily Cooper makes a case for overturning the witchery laws: in all previous witch trials, it was the witcher who brought up any connection with Satan, while the defendant had been too beaten down to resist. The judge, John Adams, is sympathetic, but realizes that a sudden overthrow of long-kept laws will cause social instability.
Calvin has come back to America from France with Honoré de Balzac, the French boy-writer. The two meet up with Peggy and Calvin gets himself in serious trouble.