After a fun time at a bowling alley with Conan and Sonoko, Ran realizes that she needs to the bank because her father wanted her to cash a check from a client. The nearest bank is Tohto Bank, so they head over to that bank.
Ran, Sonoko, and Conan sit down next to man (Saburo Tsuji) listening to a cassette tape through his headphones. At the door, a bank employee (Takashi Nagai) is thank youing customers. He is wearing a face mask because he has a cold. Kazuo Ebisawa, the bank branch head, recognizes Sonoko (her father being the head of a large corporation) and greets her. Conan coughs, and another bank employee, Noboru Taniguchi, offers some cough drops. Tetsuya Maejima, yet another bank employee, tells Ebisawa that he is going out back as he puts his cell phone into his coat pocket.
As Maejima opens the back door, a man with a helmet on forces his way in, knocking Maejima unconcious. The helmeted man points a gun on everyone and tells them to raise their hands. He orders Taniguchi to start stuffing his bag full of money. Tsuji starts to record everything that's going on with his tape recorder. The assailant starts coughing and reaches into his pocket to find trash. He throws that onto the ground. He then sits down into a chair with a coat hanging from it and digs into the pocket, searching for something. During that time, Maejima regains conciousness and tries to whack the gunman over the head with a large stick, but a cell phone rings, and the gunman turns around and shoots Maejima. The gunman is upset at this and starts yelling for the people to shut up. Taniguchi takes on the gunman, the gunman is shot and goes down.
The police is called. Maejima is sent to the hospital, but there is no risk to his life. Megure goes over the facts. When Maejima tries to hit the gunman with the stick, his cell phone rings (which is in a plastic bag now). That's when the gunman turned around and shot Maejima. Taniguchi panicked and took on the gunman. He didn't want the gunman to shoot anyone, and during the struggle, he tried to point the gun another way when it went off into the gunman. Conan sneaks around the area and notices that the gunman also had a cell phone on him. The gunman's name is Tohru Saeki, born Showa 45 (1970). Takagi shows the driver's license to the people in the bank, asking them if they recognize him. None of them recognize him. A cell phone rings and every reaches for their own, but it turns out to be Maejima's. Megure answers the phone and asks the person on the other line if he called earlier, but he didn't.
Conan goes up to Tsuji and asks if he could listen to the tape. Tsuji lets him only if he keeps it a secret. He wants to sell it to the news to get lots of money from it. Conan listens to the tape, and confirms what he already knew.
Megure tells the bank employees that nothing will happen to Taniguchi since he acted out in self-defense. Megure also believes that if the random call on Maejima's cell phone didn't occur, things could have ended differently.
Conan does some more sneaking around. He picks up Saeki's cell phone and lets it ring before it's taken away by a crime scene investigator. Megure wants to take Taniguchi to the police station for routine procedure. Taniguchi agrees, but he want to go to the restroom first. In front of the restroom, Taniguchi takes out his cell phone to do something when Conan appears in front of him. Surprised, he goes into the restroom. Conan walks around inspecting the doors and stuff. The doors from the outside are all secured with card key entry locks. Conan remember that the gunman was digging around in Taniguchi's coat and that he threw something away just before he started digging around in the jacket. On the ground he finds what he was looking for.
Using Sonoko again to play detective, Conan shoots her with his stun gun watch and hides. He tells Megure, through Sonoko, that the phone that rang wasn't Maejima's but the gunman's cell phone. Megure asks Sonoko how she knows. She/he tells him that it was the difference in ringing sound. Conan tells Megure about the recording that Tsuji made. They listen to the recording and they listen to the ringing of the cell phones. The person who made that phone calls wasn't just some random guy, either, it was the gunman's accomplice, Taniguchi.
When Maejima was leaving throught the back door, Taniguchi called Saeki to alert him that someone was going to leave through the door. When Taniguchi was stuffing the bag full of money, Saeki hardly looked at him. But when Maejima regained conciousness, Taniguchi couldn't just let Maejima knock Saeki out, so he called Saeki's cell phone. Taniguchi didn't expect Saeki to shoot Maejima, so he freaked out when Saeki did. Realizing that things had gone terribly wrong, Taniguchi jumped Saeki and killed him, effectively making sure he wasn't caught up as a suspect and making it look like an accident/self-defense.
Megure asks to see the phone, but Sonoko tells him that it's useless because the redial number was already erased. Instead Conan presents two pieces of cough drop wrapper. One is the one that Taniguchi gave Conan, the other is the one that Saeki threw away. Evidently, Saeki and Taniguchi met earlier that day. They split the package of cough drops. When Saeki was coughing during the heist, he pulled out the drops, not realizing that he ate them all up already. He knew that Taniguchi had the other half, so he searched Taniguchi's jacket, not realizing that Taniguchi gave the entire half to Conan. The two halves fit. The wrappers also have both Taniguchi and Saeki's fingerprints as hard evidence. Turns out that both men wanted to rob the bank because each had a debt to pay off and to have some play money.
And so, Conan, Ran, and Sonoko walk away...with Sonoko's ego a little bigger....