One day, while Doraemon is taking a nap, his bell is stolen. The person who stole Doraemon's bell is mysterious thief DX. By using a Sherlock Holmes set, Nobita discovers that a clue for the case is at a secret tool museum, which is in the future. So, they decide to all go to the future. At the secret tool museum, various secret tools have been stolen by mysterious thief DX.