(SPOILER WARNING: Reading this series reveals the plots for some of the coolest episodes. I suggest waiting and watching them yourself, so read at your own risk.)
(Apology: Forgive me if some of the things in here are incorrect. My Japanese is only basic, so I have to make guesses at some of the things that happen.)
The episode begins with Ran telling Conan about a play she will soon star in, opposite a very attractive male lead (there's even a kiss scene). As Ran heads off to the shower, Conan smolders, and this does not go unnoticed by a slightly upset Ai.
Scene change. Dr. Agasa has decided to take The Detective Boys, Conan and Ai (who still seems slightly upset at Conan) on a short camping trip. As they make camp, Conan and his school buddies go off to fetch firewood, while Ai and Dr. Agasa stay behind to begin making dinner. On their way back to their campsite, Conan and trio find a large cave, with an odd sign outside. Ever curious, the detective boys want to investigate, and after his protests are ignored, Conan follows to keep them out of trouble.
Inside the cave, they hear the sound of people's voices, and without thinking, Genta rushes ahead to greet these fellow spelunkers. Unfortunately, he is greeted with the sight of three men in the process of disposing of a corpse. Not known for being stealthy, Genta is spotted, and a baddie fires his gun at the kids, now running for cover. They find a temporary hiding spot, and it's then that the detective boys notice. Conan's been shot.
Still conscious, Conan pulls together the frightened children and tries to use his communicator to contact Ai. Unfortunately, Ai is out of earshot from her communicator, so the kids make a desperate charge for the exit, being followed by the baddies. When they come to a fork in the path, Conan (piggy backing on Genta) has an idea.
The baddies soon arrive at the fork, and notice a light that's been dropped on one of the paths. The henchbaddies are about to go that way when the head baddies points it out as a deception, and they take the opposite path. Coming back to the kids, they question Conan if going down the same path as the light was a good idea. Going further down the path, they are suddenly attacked by bats. Realizing it's his communicator they're after, Conan dumps his into the corner and the bats fly away. They soon reach a branch where there are four exiting tunnels and a rock with a stone egg resting on it. There is a clue as to the exit, but just as Conan is realizing the answer, he passes out. The baddies are once again approaching, and without the help of Conan, the detective boys must figure out what to do to save all their lives...