When Navy Lieutenant, Clea Thorson, is found dead after running onto the street and into an oncoming bus, Ducky discovers chemical symbols and codes written in thick black ink all over her body. The autopsy reveals that Clea was actually being slowly poisoned and which caused her to become increasingly paranoid and sick. Clea, a brilliant engineer, was recently fired from a bio-tech company working on a very lucrative project to help the Navy become more fuel independent. Her former boss Dean Stillwell said that Clea was a genius at what she did but became increasingly impossible to deal with. Clea's mother explains that her daughter was on medication all her life to control her mood swings and manic behavior but recently felt that Clea was in danger. Clea recently started sending her mom large amount of money incase anything happened to her. Abby soon becomes intrigued and almost obsessed with trying to decipher what these codes from Clea's body. She retraces Clea's route on the metro and finds herself at Clea's university where she meets up with a professor that Clea trusted. Clea's old co-worker, April Ferry, secretly comes into NCIS to drop off some files hoping it may reveal more information into her death. We discover that after Clea was fired she went to work for Stillwell's biggest competitor and was paid under the table. Things get complicated when her old boss and lead suspect Dean Stillwell is found dead..Clea's killer turns out to be her old co-worker April who was jealous of all of Clea's accomplishments. April poisoned Clea with a type of ethanol that she attempted but failed to patent because the fuel left a deadly by produce of formaldehyde. April attached a canister of the poison to Clea's main water line slowly poisoning her every time she showered.