A Naval Reserve lieutenant in mufti dies of a single gunshot to his head in a public park in Washington, DC; Gibbs and company investigate; the victim has a business card bearing the name of Timothy McGee, who learns that his paternal grandmother, Penny, is involved with the vic; Tony and McGee intercept Penny and talk with her. The victim teaches math at a local university and works for a think tank in the boondocks of Virginia. Abby figures out the burns on his fingertips. Attention turns onto Penny, who survives three attempts on her life, and who proves to be a tough nut. The gang put all the pieces together and catch the bad guy, then Penny gets a ride home with Ducky, and McGee calls his father.