Father Michael Keogh (John Mills) is a dedicated Catholic priest who arrives in a sleepy Mexican village to be confronted by a murderous gang of bandits led by Anacleto (Dirk Bogarde). To intimidate the newcomer, Anacleto's gang set out on a series of murders of local villagers. The gutsy priest resolutely decides to challenge Anacleto's power and a struggle ensues. Despite their differences Anacleto develops a grudging respect for Father Keogh and is anxious to determine whether it is the 'singer' (the priest) or the 'song' (religion) that inspires good. As their relationship develops Anacleto realises that the beautiful Locha (Mylene Demongeot) is in love with the priest who is struggling to control his feelings for the woman. Anacleto uses this knowledge to create a situation that forces the priest to face up to his feelings for Locha and leads to a dramatic confrontation between the two men.