This episode had the team involved in various aspects of a secret exercise to smoke out the mole among them. Playing to NCIS's reputation for unpredictability, McGee, Tony, and Ziva had no idea of Ducky or Abby's roles in the plot. With each twist, you had to wonder what the truth was. Meanwhile there was some great humor in how each character handled the tension. I particularly enjoyed its effect on Tony and Ziva's as-yet unspoken feelings for each other.
I sure hope Agent Lee is being compelled to spy and isn't simply playing everyone with her confession. Her body language when no one is looking, cute nervous as always, suggests the former.