This week's 48 HOURS centers on SURVIVOR contestant Joe Hunter, whose emotional tribute to his late sister Joanna became one of the most talked-about moments of season 48. Joanna's death was officially ruled a suicide, but Joe says she was murdered and has made it his mission to uncover the truth. 48 HOURS correspondent Natalie Morales has the story on what happened to Hunter's sister in this episode, "Joe Hunter's Mission."

When a gravely ill young woman is rushed to the hospital, doctors make a shocking discovery: she has an "astronomical" amount of lead in her body. What begins as a medical mystery quickly becomes a criminal investigation. Hannah Pettey, a young mother from Alabama, suffered debilitating pain and lost more than 45 pounds in the months prior as her health rapidly declined. Investigators focus on the two people she trusted the most as the police work to uncover who was poisoning Hannah, and why. 48 HOURS correspondent Anne-Marie Green reports on the case in "The Gaslighting of Hannah Pettey," which includes Green's multiple interviews with survivor Hannah Pettey and an exclusive interview with the prime suspect in the case, Hannah's husband, Brian Mann.