NCIS's season 4 begins in uncertainty as the team recovers from the emotional turmoil caused by an injury Special Agent Gibbs sustained while on assignment. Gibbs, a former Marine gunnery sergeant whose skills as an investigator are unmatched, formerly led this troupe of colorful personalities. A man of few words, he needs only a look to explain it all. The team includes Special Agent Anthony DiNozzo, a frat-boy type whose instincts in the field are surprisingly strong, Abby Sciuto, a scientist whose wit matches her Goth style and eclectic tastes, Special Agent Timothy McGee, an MIT graduate whose brilliance with computers overshadows his insecurities in the field, and Ziva David, a former Moussad agent who shares a special bond with Gibbs. Assisting the team is medical examiner Dr. Donald "Ducky" Mallard, who knows it all because he's seen it all, and he's not afraid to let you know. Rounding out the team is NCIS director Jennifer Shepard, who has a romantic history with Gibbs. Despite the stresses of the job, humor remains a mainstay for the members of the NCIS team, and they keep things light even as they hunt for some of the most dangerous criminals in the world.