Katie Watson and the Serpent Stone

This second book in the Katie Watson Mysteries in Time series whisks readers, along with Katie and her cousin Imogen, back in time to the wild American frontier of 1828. In a world teeming with dangers, from renegade Indian warriors to horse thieves and bandits, Katie and Imogen team up with a young half-Cherokee Indian Wattie to survive.
But, Wattie's village is under attack, and at the heart of the Cherokees' troubles is a stolen stone: the legendary Serpent Stone. Embarking on a dangerous river voyage to solve the mystery of the stone could save Wattie's home. But, Katie has a hunch that the quest might also lead her to discover, who is behind the time-portal paintings.