Episode 18: Mom's Treasure!/Maru-chan's Late Night Feast!
Original Airdate: May 6th, 1990
Maruko accidentally loses her mother's valuable opal ring. Then, entranced by classmate's tales of waking up during the night to find adults eating delicious treats, Maruko vows to catch her parents in the act one night as well.
Timing help provided by Mr. Manager.