Based on

Movies like Two Against All (1962)

Two brothers, Bull and Jonathan Bullivan, witness the murder of bandit Black Boy who had been terrorizing Golden City. The bandit had been put in place by the city mayor, who wants the local residents to leave so that he can keep their land, where there is oil. The two brothers eat a chicken that has been fed with a strong tonic and they become sort of invincible for a few minutes. The mayor, pressured by the villagers, appoints the Bullivan Brothers as sheriffs and tasks them with the arrest of Black Boy.