Rule 91 is the sixteenth and final episode of NCIS Season 18 and as well as the 414th episode of the entire NCIS series.
This episode also marks the final appearance of Emily Wickersham (Eleanor Bishop) as a main cast member.
While pursuing a dangerous arms dealer, the team is shocked when Bishop is implicated in an old NSA leak while Gibbs and Marcie realize the killer they've been tracking may be onto them.
- Bishop resigns from the team and NCIS.
- Rule 91 is revealed to be "Walk away and don't look back".
- Randall Pink Mr. Flori's food ordering name is a reference to the character in Dazed and Confused Randall "Pink" Floyd
|Leroy Jethro Gibbs||Mark Harmon||Ex Special Agent Assigned to NCIS Major Case Response team. (Indefinitely Suspended)|
|Timothy McGee||Sean Murray||Senior Agent for the NCIS Major Case Response Team. Currently in charge.|
|Eleanor Bishop||Emily Wickersham||Special Agent for the NCIS Major Case Response Team.|
|Nicholas Torres||Wilmer Valderrama||Special Agent for the NCIS Major Case Response Team.|
|James Palmer||Brian Dietzen||Chief Medical Examiner for the Major Case Response Team.|
|Kasie Hines||Diona Reasonover||NCIS Forensic Specialist.|
|Leon Vance||Rocky Carroll||Director of NCIS|
|Donald Mallard||David McCallum||NCIS Historian. Despite being credited, McCallum doesn't appear in this episode.|
|Marcie Warren||Pam Dawber||Journalist.|
|Jessica Knight||Katrina Law||NCIS REACT Special Agent.|
|Odette Malone||Elayn J. Taylor||An old friend of Ziva's. Planning on leading an undercover operation with Bishop.|
|Afrim Murati||Rafael Petardi|
|Ronda Ellis||Donzaleigh Abernathy||NSA Deputy Director.|