When Lassiter returns from Surprise Valley, what do he and Jane discover about her horses? Why is this important? What does this mean to Jane and Lassiter?

When Lassiter returns from Surprise Valley, he and Jane discover her horses are gone. This is important because the horses are Jane's last hope of escape. She knows these horses can outrun any other horse, and without them she and Lassiter may not be able to make their getaway.