Weeks after being reported missing, a woman with a rare disease resurfaces in suburban Massachusetts and inexplicably causes excruciating pain and subsequent death to those she encounters. As the gruesome scene is investigated, dangerous levels of radiation are detected, and unusual circumstances surrounding the case point to illegal human drug trials, and possibly something even more sinister. Meanwhile, Walter obsesses about cotton candy, Peter strikes a bargain with Nina Sharp, and a startling piece of Olivia's past is revealed.