第90話: のび太とドラえもんは、家族のダイヤモンドの指輪の盗難を防ぐために過去へタイムトラベルする。

90

Nobita leaves a photo album on the floor. The book brought nostalgia to Nobita's mother and she recalled a story about a precious diamond ring that was passed down in their family, but was stolen by two boys. Nobita and Doraemon go back in time to stop the robbers. The diamond ring turned out to be plastic and was meant for Nobita's mom to be a lesson. (Source: Wikipedia)