If this episode title made you think the case is connected to a wedding, then you are correct. In the early years of the series, there was a canon story in the manga about Ran and Shinichi’s teacher getting married and becoming the victim of an attempted poisoning.
In this episode, Kogoro and Conan are at a wedding (Kogoro was invited because he met the groom’s father at a bar and became friends with him, and Conan was asked to come along). As the bride is walking down the aisle, she suddenly declares she can’t breathe, and then collapses. Kogoro checks on her, but pronounces her dead. As this is happening, Conan overhears people at the altar making comments about the bride.
When Takagi and Chiba arrive at the crime scene, Takagi notices Kogoro there and asks something along the lines of how Kogoro managed to be at the scene of the crime. This is when we get the explanation for how Kogoro and Conan were invited to this wedding. Takagi and Chiba make some off-hand comments to themselves about Kogoro and how he always seems to be at crime scenes. At this point in the series, I can’t blame them for having these kinds of reactions.
Pretty quickly, it becomes clear that the bride was poisoned, and that the poison that was used will kill someone within a hour of ingesting it, even if it’s a small amount. This whittles down the potential suspects to people who could have given the bride something to eat or drink within an hour of her death.
As the investigation gets underway and potential suspects are questioned, a portrait emerges of the bride… and it turns out her actions over the past few years have earned her a lot of enemies. As we see during the questioning, the suspects turn out to be the people Conan overheard at the altar. When each of them is questioned, Conan asks them why they said what they said. Between these answers, what Conan picks up on while accompanying the adults, what Conan picks up on his own, and from what he has Takagi look into (in the guise of Kogoro asking for this to be done), Conan figures out the truth behind the murder right at the halfway point of the episode.
The remainder of the episode sees everyone being gathered at the altar, Conan using the stun gun and bowtie trick to reveal the truth, and what happens in the aftermath of the revelation. I don’t want to reveal who the guilty party is, but what I will say here is that it was the person that I had least been expecting to be the culprit. But after everything is explained, this person had a motive that didn’t feel forced.
This was a decent single episode murder mystery, but I am still a little frustrated by the fact that it reuses the idea of poisoning a bride at her wedding. Yes, the outcomes were quite different between the two stories, but the basic premise felt like it was being recycled.
From looking at a Detective Conan wiki that has an episode listing, it shows that for the next couple of weeks, Japan will be getting a rerun of an earlier two-part episode. Whenever that happens, that means there won’t be a new episode to watch as a simulcast. And then the following two Saturdays will be Christmas Eve and New Year’s Eve, and I’m not sure that new episodes of Case Closed would air on either of those Saturdays… although between those two Saturdays, there’s a greater chance of something new being aired on Christmas Eve than on New Year’s Eve. I’ll keep an eye on that wiki to see what, if anything, is listed for December 24 and December 31.
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