Kogoro, Ran, and Conan are staying at a hotel when they run into Kogoro's estranged wife, Eri Kirisaki. Eri is at the hotel with colleagues of hers. Kogoro is upset seeing Eri around another man and proceeds to get drunk. He is later found in the bed of Eri's female colleage, who has been murdered!

A man dies right in front of Conan, Kogoro, and Ran while riding on a bus. What does a past murder on the bus have to do with this one?