Conan, Genta, Mitsuhiko, and Ayumi went to a exhibit of hidden treasure. They find a piece of paper with on there the words "Oro". A treasure hunt begins, while Conan is not interested in the map until he discovered that Oro means "Gold" in Italian. Later they figured out that neo-signs got something to do with and that the mafia is chasing them which they think that Conan and the others can lead them to the gold. After solving the treasure hunt, it was stolen gold which the mafia came and kept Conan and the others captivate. Conan came up with a plan to make them fallacious with succeeded and told a nearby kōban to tell the officers about the criminals they've caught. They told the story to Ran which Genta and Mitsuhiko started to brag about it. Ayumi told Ran that nothing was done by Genta and Mitsuhiko but by Conan, which she gives him a kiss on the cheek, which makes Ran thinks that Conan got a girlfriend. Genta and Mitsuhiko are staring at Conan being in jealously.

Kudo Shinichi is a seventeen year-old high school detective whom people call the "Modern Sherlock Holmes." However, one night after a date with his childhood sweetheart, Ran, Shinichi witnessed an illegal trade and, caught off his guard, was knocked unconscious and fed a drug that was supposed to kill him... but he woke up and found himself shrunken to a seven year-old. In order to track down the men who did this to him, Shinichi hid his identity and lived with Ran, whose father happened to be a hopeless detective, and with that came a series of murders and mysteries that he must solve.