Medical examiner Sonya's life is in jeopardy when she is exposed to a mysterious poison as the CSI team races to find the antidote and the silver ink murderer who appears to be targeting the Crime Lab. Max's ex-husband, Daniel, returns to make sure that she and their son are safe.

When the body of a young girl who was killed over 40 years ago is discovered at the bottom of Lake Mead, Max Roby promises her mother, Raquel Williams, that the CSI team will finally find justice for her daughter. Also, Greg Sanders brings his quirky humor as he returns to the crime lab.