Lilly investigates the 2003 case of an autistic boy who witnessed his parents' murder.
The team questions the credibility of a former FBI agent's bizarre account.
Hours after calling Gibbs about a possible case, a Marine is found dead in Quantico; McGee and Bishop pose as a married couple.
Don and Megan hunt for a former chemist who is thought to be tampering with over-the-counter medication, causing many people to suffer seizures.