<P> Set over the course of several months, the episode follows a series of events surrounding the investigation given to Special agent Tony DiNozzo by SECNAV Clayton Jarvis (Matt Craven) in "Pyramid", culminating in the death of an NCIS agent . Secretary Jarvis assigned Tony to the investigation after a dead Navy Captain was found with an incision in his arm . After Dr. Donald "Ducky" Mallard discovers security footage of Special agent Erica Jane "EJ" Barrett removing a microchip from the body of Special agent Gayne Levin, suspicion falls on her . </P> <P> The Major Case Response Team begin to suspect EJ is the target of Tony's investigation, but EJ confides to Tony that Levin asked her to remove the microchip . The team learns that the microchips provide access to a classified Navy fleet, known as the' Watchers' . Tony is lured to a meeting with EJ and her buyer, revealed to be Barrett's other team member and the target of Tony's investigation, Special Agent Simon Cade, although he claims that he was framed . During the meeting, all three are shot . Cade is killed, Tony is knocked unconscious and Barrett is missing . As Tony recalls the meeting, he realizes they were set up by the shooter, an FBI agent in league with the Office of Naval Intelligence's Director of Special Operations, who places the microchips up for auction . </P> <P> "Nature of the Beast" is written by Gary Glasberg and directed by Tony Wharmby . Glasberg thought about the main storyline at a hotel in Las Vegas, ending up with the idea involving Special agents Simon Cade, Gayne Levin, Erica Jane "EJ" Barrett and Tony DiNozzo: "Cade is the one in the picture, but he didn't do it . The audience needs to think EJ is the one in the photo, but she isn't the traitor either . Yes, she took the microchip from Levin, but what if she did it for well - intentioned reasons? What if the whole thing was a set - up?" About how to make Tony remember, "why not bring Dr. Rachel Cranston back? She could help Tony remember what he'd done . She and Gibbs could help him put the pieces together", Glasberg say . "I knew (...) Tony, EJ and Cade needed to all be innocent pawns in someone else's larger plan . And that's how Stratton and Latham (Scott Wolf and Phil Casnoff) were born . New villains for an exciting new season". </P> <P> The episode includes a lot of recurring characters, some for the first time and some for the last time . Jimmy Palmer (Brian Dietzen), E.J. Barrett (Sarah Jane Morris), Rachel Cranston (Wendy Makkena) and Clayton Jarvis (Matt Craven) continue their participation on NCIS, while Scott Wolf's Casey Stratton is shown for the first time . Matthew Willig ends his recurring role as Special agent Simon Cade . </P>

Who is tony after in ncis season 9