An investigation into the death of a marine leads to a dubious weapons deal (21/23).
The death of a marine unearths a top-secret military research programme. Meanwhile, Abby is called away to assist with an ongoing medical project.
The team learns that ten kilos of highly toxic chemical weapons have fallen into the hands of a terrorist and races against time to stop him.
Gibbs teams up with an old foe, CIA agent Trent Kort, to hunt down an international criminal at the top of NCIS's most wanted list.