A teenage girl loves to tease and scare her easily-frightened younger brother. One day a mummy is delivered to their house from their father (who is an Egyptologist). When their mother leaves for a few hours, the sister cannot resist the temptation to see a real mummy and opens the sarcophagus, in the process (unbeknowedst to her at the time) awakening the long-dead mummy.
Later she dresses as a mummy herself to frighten her brother and has a good laugh at his fright. Immediately the "real" mummy appears, and the brother, still angry at his sister's prank and assuming it's another trick, confronts the mummy, ultimately becoming the hero of the episode.