When Dorothea's charitable work brings her to Oakgate Prison, she is delighted by the chance to explore her fascination with phrenology and test her hypothesis that the shape of a person's skull can cast a light on their darkest crimes. But when she meets one of the prisoners, the teenaged seamstress Ruth, she is faced with another strange idea: that it is possible to kill with a needle and thread--because Ruth attributes her crimes to a supernatural power inherent in her stitches.