The ruthless and cruel Captain Ramirez hunts down and kills revolutionaries in his search for The Saint, the righteous leader of the Mexican insurrection against the Federales. Adding complications to Ramirez's pursuit, a group of American gunmen secretly steal weapons from US encampments to be sold to the freedom fighters. Killer Kid, the most dangerous gunfighter in the west, manages to escape from a military prison and soon ingratiates himself in the company of the elusive Saint ultimately joining them in their fight against Ramirez. However, one of the Saints men, Vilar, doesn't trust the American ace gunfighter whose motives and actions are shrouded in mystery.
Killer Kid stars Anthony Steffen as a US agent impersonating a famous gunfighter known as Killer Kid who has a lot of conflicts with Fernando Sancho, a revolutionary soldier with bandit tendencies, making you think they'll have a showdown at the end, but they eventually find out they're on the same side - the actual enemy is Captain of Mexican Federales (Giovanni Cianfriglia) who orders reprisal executions of innocent peasants in order to make anyone in the peasant village reveal where the revolutionary leader El Santo is hiding.
It's a decent Zapata western with plenty of gunplay and less political overtones, thankfully. There's a little poignancy in the drama and some good acting, especially by Fernando Sancho. Steffen's change to a person helping the cause of the revolutionaries could've been done better but hey the beautiful daughter of the Saint played by Luisa Baratto is a good incentive enough.