Powderkeg (1971)

⁣A Mexican bandit is about to be executed in the United States. So his brother takes over a train and holds the passengers as hostages unless his brother is released. Now both the Americans and Mexicans are baffled as to what to do. But one of the passengers, who wrote the letter for their captor, has a suggestion; call Hank Brackett and Johnny Reech, two mercenaries.