[WATCH] 'NCIS' Sneak Peek: Abby's Goodbye Begins

NCIS season 15 episode 21 is the first of the two-part goodbye to Pauley Perrette. In it, Abby is awarded a dinner reservation for two to a brand-new five-star restaurant in an igloo and must decide which coworker deserves to go with her.

As for the case in "One Step Forward," a woman, Sara Carter (guest star Skye P. Marshall) begs Gibbs to investigate her mother's murder. She believes that the local authorities convicted the wrong man.