The episode where everyone at NCIS learns about Gibbs having a wife and a child before the three marriages they had been aware of.
In addition to learning that Gibbs was previously married and together they had a child , the details of their demise is also explained which sets the stage for a few future episodes concerning the fate of the person responsible for their deaths and the ensuing investigation.
In a parody of Gibbs' rules, DiNozzo declares his rule number 3 to be: Never underestimate your opponent.