S6·E12 Nerves

Wendell Hayes, the brother of an imprisoned Syndicate enforcer, has stolen a canister of nerve gas and threatens to use it if his brother Cayman isn't freed - the IMF must stop him and recover the gas. Worse, the canister has a defective casing that Wendell is unaware of, and will release the gas in 43 hours anyway. And...Cayman dies of a heart attack in jail, forcing the IMF to have guest-agent Bill Williams take his place. The IMF has Hayes' imprisoned girlfriend Saretta ""escape"" with prisoner-Casey handcuffed to her. Saretta takes Casey to a winery in a IMF car with a bug on it that Barney traces. Jim delivers ""Cayman"" but Hayes doesn't turn over the gas. They track Hayes to an observatory but he gets word via his partner Tully that his brother tied and he unmasks Williams-as-Cayman. Hayes and Tully shoot it out over an argument and with his dying breath Hayes tries to shoot open the canister...hid in the observatory roof, revealing its location to the IMF.