Nobita is daydreaming about catching and solving the mystery behind Kaito Lupin as Sherlock Nobita. But he slides up in the balcony and cuts out of his daydream. He caught up in the conversation of Suneo, Shizuka and Gian in their classroom. As usual, Nobita is abandoned about not to come. Back at Nobita’s house, Doraemon starts to sleep in his closet for a rest while waiting for Nobita. And then a scene where a robotic hand next to the desk appeared. It left a “DX CARD” in Nobita’s room right before he entered. He threw his bag in the tatami and the 0% test paper flew out. He notices the DX CARD but was interrupted when his mum called him. He is alerted about the test and accidentally crumpled it with the DX CARD. His mum said to him to eat his snack in the kitchen while seeing enviously. After the both of them left the room, Doraemon is in his closet sleeping while a robotic hand tried to reach up for his bell. It took the bell and escaped in the time hole. Doraemon panics about his cat bell.
He consulted Nobita about the incident. Then Nobita asked what the importance of the bell that he’s been hanging in his neck is. Doraemon checks it up in the factory where he had been made and asks if he could repair the cat bell. But the employer can’t do it because it is now a substandard type and a piece of junk. Doraemon gets frustrated and takes the bell back in his neck. Then Nobita said, “If the bell is the problem, we’ll replace it”. He gets the “Kisekai Camera” inside the Pocket. Nobita tries different items that resembles the cat-bell such as Christmas bell, gondola’s bell, banana, Chirps, egg yolk, and a cough neck. Then Nobita saw Doraemon act as a cat, and he realizes that “if something is lost, you use that gadget”. Doraemon takes out the “Sherlock Holmes Gadget”. With that they can easily find the bell and the culprit. They first use the Finder Pipe to find the culprit easily with the bubble it produces, but it won’t work. However using the Magnifying Glass and Sherlock Inference hat, Nobita get the name of culprit called Kaitou DX who is well known classic Gadget thief in the 22nd century. Consulting the incident with Dorami, Doraemon and Nobita, along with others travel to the 22nd century to visit the Gadget Museum where they meet Director Fiks and Kuruto Harutoman aka Kurt, a young guide of the museum. Kurt give the groups the tour of the Museum where Doraemon and Groups were amazed to see the invention made by the people of the 22nd century. They were fascinated by all the tools and most of all, they saw the very first “Anywhere Door” ever made! However while the Group were having fun, Doraemon and Nobita try to search their lost bell which let them to the pond where they were asked to catch “Baba Robot” however one of the robot accidentally get into Doraemon’s pocket which render him unable to use his pocket.
Fascinated by the creation of the Gadget, Gian and Suneo unknowingly passed through the shrinking tunnel, resulting in shrinking to small size while Nobita, Doraemon and Shizuka get lost into the tunnel leading them to “Natural Man Made Solar Sun” from which the whole museum works. Due to Dr. Pepura Hasake (which is been shown the reason why he secretly lives inside the secret room along with his grand daughter Ginger) negligence, causing a freak accident which result to the solar sun going mad and endangering the world leading him to get dismissed from his post and leaving the museum. However, due to this incident, Dr. Harutoman (Kurt’s grandfather) discovered the metal named as “Fullmetal” which enable him to stabilize the core of the sun and made him famous.
Doraemon starts acting more and more like a feral cat which makes the groups to stay a night at Kurt’s home greeted by his pet “Poppo”. At his home, Nobita accidentally starts a super-vacuum, which sucks all of Shizuka’s clothes, leaving her completely naked, while everyone sees her naked butt. The next day, the museum got the threats from “Kaitou DX” declaring to steal four gadget items at noon. Even though the security and police were tightened, Kaitou managed to defeat Doraemon and groups and successfully stole the listed items. To understand why Kaitou DX stole the listed items, Nobita with the help of Sherlock detective gadget, they came to know that the listed security context were repaired on the same day when Dr. Pepura was captured. The group decides to find him, which led them to the secret way. However, they encountered Head of Gorgon, attacking the group with laser which turns the people who is hit by the laser to stone. Shizuka and Nobita managed to beat it by turning the head itself into stone by using a mirror. During the incident, Kurt’s monitor was recovered by Nobita. When Kaitou intercepted the group, Nobita managed to discover the real identity of Kaitou which in turn known to be Kurt himself. Kurt reveals himself as the Copy Robot who took his place. When asked about the reason, Kurt explains the discovery that he and Dr. Pepura were about to create. In order to convert all the FullMetal into Pepura-metal, he needs to recover the chips which Dr. Pepura hides it under the six lost items while they were at repairing stage. So to recover them, they created Kaitou DX and spread the rumors to carry out the purpose.
While the truth is revealed, Dr. Pepura recovers the chips and begins the process. Kurt manages to outrun Nobita and other. However being shrunk in small size, Gian and Suneo manage to slip into the door and recover the Magnificent Light which restored them back to their normal form. Even though the team reached, it was late as Dr. Pepura has already begun the process. However the process failed as the FullMetal when converted into PepuraMetal started to deteriorate. This resulted in releasing the monstrous protector which escaped from the prison and attack the group who were trying to control the man-made solar sun after the machine failed to stabilize the sun. While fighting both the situation, Doraemon accidentally wore the Kaitou’s Bow which make him into “Kaitou Dora DX”. While Doraemon engages with the security monster, Nobita and others try to stabilize the growing sun. Doraemon manages to defeat the monster but accidentally destroys the mainframe that controls the system of the sun. When all hope was lost, Nobita gets an idea by ordering Poppon to suck the sun. Poppon sucks the sun and manages to make it disappear. Nobita recovers the security context (as Dr. Pepura manage to reverse the process by converting it back to full metal) while Doraemon and Kurt repair the museum (using the recovering torch and magnificent lamp) as well Doraemon’s Bell where he understood the reason why Doraemon cherishes the bell as it contains the memory of Nobita and Doraemon’s friendship.