NCIS - Nature Of The Beast

WOW!  NCIS is back!  With a BANG!  Season Nine kicks off with Tony DiNozzo, played by Michael Weatherly, in hospital with the possibility that he may have been responsible for the death of an NCIS agent.  Trouble is, we don't know which agent!  Tony's not talking, or can't remember. Last season, Tony was given an assignment from SECNAV to investigate another NCIS agent, but we don't know who.  Could it be Agent David?
Tony is visited by Gibbs, a psychologist and an FBI agent, played by Scott Wolf (from V).  Slowly, the psychologist gets Tony to open up and talk about his assignment, which was to investigate Agent Barrett, whom he had been in a relationship with.  But now she has gone missing.  Is she the dead NCIS agent?  And did Tony kill her?  This is all tied to the microchip that Barrett removed from her own dead agent's arm last season.
Why is the chip so important?  Which NCIS agent is dead and who killed them?  What does Scott Wolf's FBI agent have to do with all of this?
A really cleverly woven story that bucks the trend of the usual incident/investigation/resolution.  Welcome back NCIS!