The culprit is Riko Mizuhashi. After the case, Shinichi feels he's reverting back to Conan, and tries to leave the place as quick as possible, but Ran grabs hold of his arm, ordering him to go with her at the hospital right now, and afterwards he'll have to tell her about his "deduction about her". She says she'll never let go of his hand up to there. Suddenly, she feels drowsy and falls asleep at once, due to being anesthetised by Ai from behind, secretly. Agasa and Ai pretend driving there by chance. Though, Ran doesn't let go of Shinichi's hand, and Agasa tells Kogoro and co Ran is very tired and they'll bring her to sleep at the professor's. Once in Agasa's car, Shinichi reverts back to Conan all the while holding her hand, and even has to paper-clip his sweater's left sleeve and side when putting it on, in order to cover his left arm and side, since he's prevented from fully doing so given his left hand is "busy". He wants to have Ran believe, once she'll wake up, that she's holding Conan's hand, and that Shinichi took some rest and then left, and that Conan has put his sweater on, since it would seem very fishy he hadn't, due to the cold.
