Kogoro, Ran, and Conan are invited by Ran's friend to attend their small birthday party. There, a woman is poisoned from drinking wine, but her wine was given after someone else took a drink already.
Murder
Location:Kojima household
Victim:Keiko Sawaguchi
Cause of death:Cyanide poisoning
Suspects:Yuki Kojima, Junji Togashi, and Kasuki Nonaka
Conan figures out the trick and proves the culprit to be Junji Togashi. Conan reveals that the source of poison was the bottom of his glass. He didn't feel the effects because he put gum syrup on top of it. Gum syrup has a higher density than wine so the contents would not mix. He would be safe so long as he did not drink the entire glass. He then intentionally grabs the table cloth and spills Sawaguchi's glass causing him to give her his own. Keiko eventually drank the contents of the wine whole and died. Togashi afterwards planned to place the poison bottle inside Nonaka's bag to frame him.
Togashi confesses and reveals that Sawaguchi was his former girlfriend two years ago. She forced him to buy expensive presents for her, leaving him in debt. She then broke up with him and engaged with Nonaka. Togashi waited for this moment to pay both people for ruining his life.