The PI Grandmother's Protege is the sequel to My Grandmother the PI. Mandy Winthrop, her boyfriend Charlie and their friends, investigate a cult that has ensnared some of their peers. When Mandy helps introverted Abbey, she meets Dr. Jonah, the charismatic leader of The Watchers. To learn more about Jonah's cult, Mandy befriends Willow Hornsby, a beautiful deaf teenager who is a member of The Watchers. This association brings Willow's mother and Mandy's father, RJ, together. When Mandy discovers a connection between her grandmother's case and Dr. Jonah, her desire for justice leads to dangerous and unforeseen consequences.