Two night guard men are patroling the Chusei Art Gallery when spot a medieval armor with red eyes walking towards them.
Ran wants to go to the art gallery because of the rumor of the walking armor. Kogoro and Conan laugh it off and they both agree that it's probably just a publicity stunt and decide not to go, but Ran convinces otherwise with her karate.
They three of them go to the gallery, Ran is amazed at the beauty of the paintings. They meet the gallery manager, Ochiai. Ochiai spots Kubota, an employee, handling a painting without gloves. Ochiai gets upset and tells another employee, Iijima, to finish moving the paintings. The gallery owner, Manaka, comes in and comments on the pathetic paintings. It turns out that the gallery is to shut down. The former owner had to sell the gallery when his company went bankrupt. Iijima tells the group that the previous owner sold the gallery to Manaka on the agreement that Manaka would continue the gallery. As soon as Manaka got the rights to the gallery, he announced that he was going to shut it down and build a hotel in it's place. Across the room, Kubota is handling some medieval armor when the helmet falls onto the floor. Manaka comments about hearing about Kubota, and manages to piss Kubota off. Kubota in anger tosses the helmet onto the cart. Ochiai doesn't seem to get angry at Kubota's actions when he leaves the room with Iijima.
Ran manages to drag Conan and her dad around the gallery, but one room is closed off and they aren't able to visit it. Later on, Kogoro and Conan are dying to get home, but Ran wants to stay a bit longer. She notices the closed room is no longer closed so they visit that room, named the Hall of Hell. One of the paintings has an armor knight walking away from the winged demon with a sword plunged through it's chest. The title being "Heavenly Punishment." Ran turns around and sees Manaka stabbed through the chest with a long sword on the wall. The police are called.
Megure comes and they explain what happened and watch the security camera video. A armor appears and kills Manaka in the video. The pause the video as the armor walks away and realize that the scene looks exactly like the painting "Heavenly Punishment." Megure asks about when the room was closed and when they went in. They watch the video again and notice Manaka grabbing a title tag off the wall, frantically write something with the pen he grabbed off the nearby table. Manaka throws away the pen and balls up the tag in his hand right before he is killed by the armor.
They go to look at the tag that is in Manaka's hand. On it, Kubota is scrawled in a messy handwriting. Kubota frantically denies it. His alibi is that he was doing something that Ochiai asked him to do, but there was no one who was with him. Kubota tells Megure that he has no motive to kill Manaka. Iijima replies that he does have a motive. Kubota damaged so many art works, that the owner wanted him to compensate for the loss. Kubota continues to deny any wrong doings.
In a corner, Conan finds a ball point pen and calls Megure over. The ball point pen was specially made for the gallery as a 50th year anniversary celebration. The pens ink color and thickness check out as the one used on the tag. Conan wonders why Kubota would choose the room he did to kill Manaka since he would have known about the security camera. Conan can't imagine it would be someone who is irresponsible enough to damage art to take the time to match up the murder to the painting.
Conan goes to the security room and watches the video again. This time, Conan notices that Manaka looks suprised when he sees the back of the tag. He then remembers that the pen that he found the tip was still pulled in. A person on the verge of death wouldn't click the pen tip back in, it's unnatural. Running to the Hall of Hell, he grabs the evidence bag that contains the tag away from a forensics technician and examines it. There are invisible scribbles on the tag made only by a dry pen.
Two police officers come in with a bag between them. They found the armor used in the murder in Kubota's locker. Kogoro comments how the armor is ruined, but Iijima reassures him that it's only a replica. That would explain why Kubota was so rough with it earlier and Ochiai didn't get angry. Iijima comments that it was lucky that only the replica was bloodied and not the original works. Conan looks at the wall where Manaka was found and notices that there isn't a painting for the tag that was there. It was as if someone was trying to make sure the art was protected from the blood. In order for the trick to work, whoever had to make sure Kubota's alibi wouldn't hold. The only one was Ochiai and that he should still have the evidence proving that he did it.
Conan grabs the guide pamphlet in Ran's hand and starts running around yelling out his immense need to go to the restroom. He goes up to Ochiai and asks him to write the directions on to the guide. Ochiai knowing that he couldn't write with the pen just stands there shaking. Conan tells everyone in his indirect manner that Ochiai is carrying a dry pen, and how unusual it is. Kogoro picks up on this and deduces what Conan already knows. The real murderer told Manaka to look at the tag on the wall, and when he did, it had the wrong person's name on it. Grabbing the pen on the table to try to scribble it out only to discover the pen was dry. When Megure tests out the pen that was found on the scene, it writes. Conan tells them that the pen that was found had it's point pulled in. Manaka never twisted the cap during his moment before death, he just threw a pen that had the pen point out. Kogoro then finally figures out that the real murderer is Ochiai, the person who has the dry out ball point pen.
Iijima tells everyone that it's impossible, Ochiai had an alibi. Ochiai tells everyone that he was meeting with someone at that time...he was meeting with Manaka at 4 o'clock, wearing the armor. Ochiai confesses to everything. He wanted to punish the man who was going to destroy the art gallery and also punish the man who was selling everything off behind his back.
In the end, the gallery continued on, bring the little amount of culture the city has...