Although she'd rather not, Ran can't avoid accepting an invitation to a Valentine's party, since her best friend Sonoko is after one of the guys in a big way.› The party is for a college tennis club, but since Wakamatsu wants to make time with Ran, and Sonoko is burning to get Minagawa to like her, Ran is trapped.› Conan overhears it all, and sneaks along, telling himself he isn't just trying to find out who Ran's going to give the chocolate candy she made last night.
[Cultural Note: Girls give boys Chocolate on Valentine's Day in Japan.› It's one of the few 'acceptable' times and places for a woman or girl to declare which guy _She_ likes.› Consequently, a guy who gets no chocolate on Valentine's day is somewhat embarrased.]
The party progresses and Minagawa manages to offend the other guys.›Conan starts out spying from outside but gets caught and Minagawa's mother invites him in. Minagawa's mother has prepared an excellent meal for the party, and things start well.
However, Minagawa has a nasty attitude, and soon offends the other two men at the party. It turns out that not only Sonoko, but Kaori and Yoshimi have brought chocolate for Minagawa. Wakamatsu trys to kiss Ran but Conan manages to prevent it. Then Minagawa goes outside for a minute and falls over dead just after tasting Yoshimi's chocolate.
Inspector Megume arrives and Ran's father shows up and they go over the case.› Yoshimi is briefly suspected, but she's too easy and doesn't seem to have a motive. Naomichi confesses, but Conan sees thru the tangle and pins the real murderer.
After the credits, it turns out that Ran wanted to give the chocolate to Shinichi. Ran gives Conan the chocolate, saying that Shinichi would forgive him, since he's tried to protect Ran from Wakamatsu's advances.