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Q.E.D., vol. 9, by Katou Motohiro. Grade: B
Geemu no Kisoku (Rules of the Game, Great Magazine, 2001). We get another non-murder mystery. This time, the shares of Roy Hills Co. plummet, and Roy, a former MIT grad, gets bankrupted. He is later seen in Shinjuku trying to sell jewelry on the streets but is being roughed up by a local gang. Touma and Kana happen by and Sou recognizes his former classmate. Hills explains that he'd gotten into a "game" with the billionaire venture capitalist, Jonas Solomon, lost, and been forced out of business as punishment. Some of the rules of the game are that if you lose, you can't talk about it, if you win you get lots of money, and if you fail, you get crushed. Hills gives Solomon's business card to Sou, and the boy tears it up saying that he doesn't want to take that kind of blind risk. So, Kana tapes the pieces together and mails a letter to Solomon. A few days later, Solomon's driver and bodyguard arrives to take the two of them to a secret castle in the mountains (looks east European). There, they meet an Italian mathematician with his girlfriend, and a pair of brilliant identical twin Chinese brothers.
(Sou explains his reasoning about why Jonas is running the game. Notice how the boy's appearance changes, making him adult-like between panels. This kind of inconsistency in the artwork is pretty common.)
Solomon explains the game: He'd given his deceased wife an expensive red diamond, which he has placed on a pedestal in the next room. Each team is to draw numbered lots, and one member of each will go into the room in numbered order and then come back out. They have the choice of taking the diamond, leaving it there, replacing it with a fake, or leaving the fake with the real diamond. Once they start, they can't quit; if they lose, they can't tell anyone else about the rules; if someone else identifies them as having the real diamond, they lose; but if they can correctly say who does have it, they win. Along the way, Kana ends up talking with Jonas and learns that his wife had once gotten really angry with him for having forgotten her out in the snow when he promised to get some coal for the eyes of the snowman she was making, because he'd gotten a business call. When the game starts, the Italian claims that he is guaranteed to win, while Touma tells him that there is one trick he's overlooked, and the Chinese brothers just repeat proverbs at each other. The next day, everyone is told that they're all wrong and that they all lose. During Touma's turn, the boy had revealed the reasons behind Jonas' game - the guy's dead wife had hidden the real red diamond because she was so angry with him, and Jonas has never been able to find it. Up until now, no one has ever won this game.
As Touma is about to leave, he tells Jonas that he understands the dead wife's final message to him. And that is, that just once, she wants him to lower his head to her and apologize. This is something that Solomon has never done before and he doesn't want to do it now.
No science this time, beyond a little bit of game theory (explaining how to win Jonas' game). Lots of great artwork of old European castles and mountains, though.
(Sou's apartment has very high ceilings.)
Itetsuku Tetsutsui (Frozen Hammer, or Sledgehammer, Great Magazine, 2001). (The title comes from a quote in the story, where a woman says that she learns something that crushes her heart like a hammer.) Some company has rented a dinner cruise boat on the Sumida river, in Tokyo, and during the cruise, three employees are surprised when a mummified arm falls next to them. The next day, Kana drags Touma to the Kachidoki Bridge, where her father is examining a very old crime scene. The Kachidoki is an old drawbridge, which hasn't been lifted in 30 years (since 1970). Trapped underneath, between the ends of the two arms, is a large pipe with a corpse inside. The police fail to find a way to pull the pipe out, so they're force to open the bridge, an event that attracts a lot of spectators, including one old woman that came from Brazil, and an old guy. When the corpse is taken out of the pipe, it's found to be wearing a watch made in 1975, and there's a piece of paper in a pocket that Touma recognizes as the Bridges of Konigsberg problem. The old man is standing near Touma and declares that he'd seen the boy giving a lecture in MIT a couple years ago. The guy invites Kana and Sou to his apartment nearby.
(Kishizaki remembers Touma.)
There, the old guy explains the Bridges problem - in the town of Konigsberg, there were 7 bridges over the rivers linking the town. The question was raised, could someone travel over each of the bridges once and only once? It wasn't until 1735 that Leonhard Euler proved mathematically that it couldn't be done. The old guy watches Sou looking at the pictures and diplomas on his wall, asks the same question regarding the 12 bridges that had been over the Sumida river in Tokyo 50 years ago but modified now that the Kachidoki bridge is lifted up, announces that he's the murderer, and challenges Sou to figure everything out. Based on the photos and diplomas, he and Kana determine the guy is Kishizaki, a brilliant mathematician. He'd married a waitress named Tae, but was almost immediately drafted into the military for WW II after that. Tae was told that her husband had been killed in the fighting, and their mutual friend, Fukamori, proposed to her to get her off the streets. Later, Kishizaki showed up at their door, but instead of getting angry, blessed their marriage. Eventually, it turns out that Fukamori was the one that filled in Kishizaki's draft papers and arranged to make it look like he was dead. So, Kana concludes that Kishizaki killed his ex-friend out of revenge.
However, Kishizaki has included several clues that revolve around a cheat involving the Bridges problem that point to a different culprit. In the end, Touma figures everything out, including the trap Kishizaki planted - any attempts to arrest Fukamori's real killer will fail. So, who killed Fukamori? Why was the Bridges problem drawn on a piece of paper and put in the victim's pocket? How was the pipe trapped in the jaws of the bridge if it hadn't been opened for the 5 years prior to the killing? What is the cheat Kishizaki uses to prove Euler wrong on the original Bridge's puzzle and how does it relate to the Sumida river variant? And finally, what was Kishizaki's real purpose to hiding the pipe specifically in the Kachidoki bridge?
=============- Spoilers ==============
Ok, yeah, the main science this time is math and topology. The cheat is to assume that all rivers have a source. If you go far enough upstream, you'll eventually get to the mouth of the river and you can go around it. The reason this is critical to the story is that the shrine where Kishizaki and Tae got married is at the mouth of the Sumida river, and there's a package waiting there for Tae - pages of her diary describing Fukamori's final days, which Kishizaki had taken. Which means that the cheat is a clue to Sou for untangling the murder mystery. If you like topology, this is a decent story for you.
Comments: Touma has several quirks. One is that he hates solving mysteries if he can avoid it. This could be attributed to his being lazy, but the fact that Roy Hills, one of his friends, was a victim and he still didn't want to get involved indicates that there's something deeper going on (this is actually explained in volume 10). The first chapter is kind of weak, since the hiding place of the red diamond isn't that hard to figure out, but the second chapter is great if you're familiar with Tokyo and you like topology. (By the way, according to the official City Chamber of Commerce page, the Kachidoki bridge has never been opened since 1970. Never. Recommended.