Voodoo, within the boundaries of the laws

As far as everybody was concerned, Theodore Merlin's stomachache was a case of minor ailment, an indigestion, a bloated stomach, after having savored two mangoes out of three received as a gift from his first cousin. By the way, the third mango mysteriously disappeared. For the patient, his days were numbered. He had an intuition: he strongly believed that he had been inoculated with the most potent poison in the world, under the cover of voodoo. He was right. However, before dying, he made his closed friend and cousin-in-law, a lawyer, swear to avenge his death within the boundaries of laws.