"The place is Mexico, just across the Texas border, a mountain village held back in time by its remoteness and suddenly intruded upon by the twentieth century. And this is Pedro, nine years old, a lonely, rootless little boy, who will soon make the acquaintance of a traveller from a distant place. We are at present forty miles from the Rio Grande, but any place and all places can be - the Twilight Zone."
A human-looking alien crash lands outside a village, and accidentally kills a police officer, and is wounded by another one. He staggers to a local bar and collapses. A local doctor removes the bullets from him, and he befriends a young boy sweeping up the floor. He gives the boy, Pedro, a gift. He says he will explain it later. The alien is cornered trying to escape and he tells Pedro to show them the gift, but they grab it from him and burn it. The soldiers shoot and kill the alien. The doctor reads what's left of the gift. It says, "Greetings to the people of Earth. We come... in peace. We bring you this gift. The following chemical formula is... a vaccine against all forms of cancer...""Madeiro, Mexico, the present. The subject: fear. The cure: a little more faith. An Rx off the shelf - in the Twilight Zone."