Dr. Smith is accosted by an interstellar gunslinger named Zeno, who happens to be his mirror-double. Zeno forces Smith to swap clothes and has him arrested by a galactic lawman. While Zeno hides out among the Robinsons, Smith is taken to another planet to stand trial and Will is brought along as a material witness. Once at the planet, Smith and Will manage to escape the lawman and find a town full of residents who fear the real Zeno, and Smith takes advantage of the mistaken identity. When another gunslinger arrives to challenge Zeno, however, Smith's cowardice blows his cover. Fleeing back to the Robinsons' planet, Smith returns with the lawman right behind him, but a problem arises when no one can tell Zeno and Dr. Smith apart.