What does Truth discover about the Bardwells when Squire appears (and disappears) in the novel, Who Comes with Cannons?

When Truth sees a man following her, she races into the Bardwell farmhouse, The slave follows and to her surprise, he is recognized. "Todd, husband, Robert. It's Squire!" calls Aunt Elizabeth. The slave drops down a secret opening near the fireplace and disappears. Squire had not been chasing her. "He knew where to come because he's been here before," Truth's aunt explains. Truth discovers that the Bardwells are part of the Underground Railroad; they help slaves escape northward.