How did Avery's great grandfather's servant revenge his master's death in the novel, Half of Paradise?

Avery's grandfather was killed by a Spaniard, who was trying to force him to sell his land for the third of its price. Avery's great grandfather was close to his servant- they were running the plantation together- and few weeks after a duel had killed his master the servant approached the Spaniard in the town, confimed his name, and then shot him dead.