A silver ink note threatening Maxine Roby's life is found at the crime lab, sending the entire CSI team to crack who is behind the notes and how they connect to other murder case.

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.