Gibbs finds that a murder victim has been using an old alias from a 20-year-old undercover operation on NCIS. "Blast from the Past" is the 16th episode of the show's 12th season.
Vance: Our intel says Sergei survived. Gibbs: What? How? I hit him. He went down. Vance: He got up. No body was recovered. And wherever he is now, knowing all this? There's a good chance he'll be gunning for us. Gibbs: Not if we find him first.