Dead Letter is the 23rd episode of NCIS Season 13 and also the 305th episode of the entire NCIS series.
This episode also marks the first appearance of future MI6/NCIS liason officer Clayton Reeves.
In the aftermath of the attack that has left one of the NCIS team's allies badly wounded and also fighting for their life in ICU, the NCIS team redouble their efforts to track down disgraced British spy, Jacob Scott, who's seeking revenge against NCIS with assistance coming from both the FBI and MI6 in the form of two new agents but everything is not what it appears to be.
- FBI agent Tess Monroe and MI6 officer Clayton Reeves are both introduced for the first time with the two assisting NCIS with the case.
- Trent Kort returns and it's revealed that he has been fitted with a glass eye to replace the one he lost during his fight against Lieutenant Jonas Cobb, the Port-to-Port killer.
- Fornell remains in a coma and also badly wounded with Gibbs stepping in and becoming the executor of the will after it's revealed that Fornell had made a "Do Not Resuscitate" clause following the murder of his ex-wife, Diane Sterling.
- The team soon discover that Jacob Scott is in fact innocent and that Kort is the one who framed Scott while also leaking nuclear intelligence to the Russians. Kort was also responsible for killing NCIS Agent Kevin Dresser and former NCIS Director Thomas Morrow, than killing a former MI6 agent and wounding Fornell in Gibbs house, framing Scott again.
- It's also revealed that Kort is no longer a CIA agent, having been fired from the agency in the previous year.
- The team are later left stunned after discovering that a farmhouse Eli David had owned has been burnt down, presumably destroying files that Eli had collected regarding Kort's actions while leaving the fate of Eli's daughter, Ziva David, a former Mossad Officer and also a former NCIS Special Agent unknown.
|Leroy Jethro Gibbs||Mark Harmon||Special Agent in charge of the NCIS Major Case Response Team.|
|Anthony DiNozzo Junior||Michael Weatherly||Senior Special Agent and second-in-command of the NCIS Major Case Response Team.|
|Timothy McGee||Sean Murray||Special Agent of the NCIS Major Case Response Team.|
|Abigail Sciuto||Pauley Perrette||Chief Forensic Specialist for the NCIS Major Case Response Team.|
|James Palmer||Brian Dietzen||Assistant Medical Examiner for the NCIS Major Case Response Team.|
|Eleanor Bishop||Emily Wickersham||NCIS Probationary Agent.|
|Leon Vance||Rocky Carroll||Director of NCIS.|
|Donald Mallard||David McCallum||Chief Medical Examiner for the NCIS Major Case Response Team.|
|Tobias Fornell||Joe Spano||An agent with the FBI.|
|Emily Fornell||Juliette Angelo||Fornell's teenage daughter.|
|Trent Kort||David Dayan Fisher||An agent with the CIA.|
|Jacob Scott||Vince Nappo||A disgraced British spy seeking revenge against NCIS.|
|Jessica Terdei||Sandra Nelson||Former Head of MI6|
|Tess Monroe||Sarah Clarke||An agent with the FBI.|
|Clayton Reeves||Duane Henry||An officer with MI6.|
|Allen Kane||Damian O'Hare||A former agent with NCIS.|
|Katrina Griffin||Mia Barron||A Doctor.|
|Angela Dresser||Adria Tennor||Ex-wife of former NCIS Agent Kevin Dresser|
|Misha Rose||Taja V. Simpson||A woman who appears in the episode.|
|Paramedic (Dead Letter)||Kamal Jones||A man who appears in the episode.|
|Einat Hadar||Salome Azizi||Reporter for ZNN. Uncredited role.|
|Squadroom Agent||Karen Mandel||A woman who appears in the episode. Uncredited role.|