Fight Club had eight rules. Moses made do with ten major ones. But on NCIS, Special Agent Jethro Leroy Gibbs (Mark Harmon) has 50 tenets he lives by. Hold on… one incoming! And it’s a biggie: The May 25 season finale, “Rule 51,” marks the first time an NCIS episode has been so directly themed around one of “Gibbs’ rules.” Naturally, the nature of the 51st rule is being about as closely guarded as Area 51. But executive producer Shane Brennan is willing to rule on some expectations.