NCIS Season 8 Episode 7 : Broken Arrow
When investigating a murder of a former Navy Commander and friend of Vice Admiral Chase, the team stumbles across a piece of an old nuclear bomb that had been lost during the Cold War. Because the victim had connections to Tony's father, they track him down and question him. Eventually, much to Tony's annoyance, Gibbs recruits DiNozzo Sr. to use his contacts to infiltrate a private party attended by arms dealers. They discover that the CEO of a salvage company stumbled across the nuclear bomb and plans to sell it on the black market. The CEO is arrested, and both DiNozzos finally reconcile their differences with one another.