It's a Numbers Game: Q.E.D. vol. 23-24 by Motohiro Katou

The first of two stories from Motohiro Katou's Q.E.D. vol. 23, "The Liar," begins with Sou Touma arriving in Taiwan to meet his parents and sister, Yuu, who secretly invited his friend, Kana Mizuhara, to come along – because their parents "wanted to meet the girl who's close to Sou." Kana really wanted to meet Sou's mysterious, somewhat eccentric parents. Only problem is that they're not at the airport to meet Sou and Yuu. When they call their parents, Yuu is told they traveled to Okinawa and want them to go there as well. But there are no planes going to Okinawa for another day or two. And every ship has been booked full.

Fortunately, they bump into Ryan Garrett, director of an IT firm, who was at MIT together with Sou and planned on going to Okinawa himself. So he offers them a ride on his luxury cruiser. Sou is not too thrilled to accept the favor as Ryan Garrett was known as "Ryan the Liar" at MIT ("...the type who sweet talks to achieve his goal") and there's always a catch to being indebted to him.

When they board the luxury cruiser, Sou, Yuu and Kana find that they're not the only passengers. Ryan invited along a handful of people. John Harris, a business partner of sorts, whose runs an IT company that's a subdivision of Ryan's firm. Al and Martha Moss are teachers from Arizona whose son was a classmate of Ryan. Lastly, there is Ryan's alcoholic ex-girlfriend, Beth Bloom, who still holds a grudge and her current boyfriend, Barry Force. Something is obviously brooding as Ryan promises Sou "there is a surprising result waiting for us tomorrow," but what awaits him the next morning is Ryan's body bathing "in a sea of blood." Sou uncovers that all five suspects possess both motives strong enough to kill and alibis accounting for their movement on the night of the murder. Sou posits that "among the five of them, there is a liar, and that lie was what brought about this whole situation," which is an incredibly good and clever solution – a twisted inversion of a very well-known detective novel. Just as impressive is Sou's Ellery Queen-like chain of deductions and reasoning demonstrating why none of the other suspects could have done it ("thus, ends my demonstration"). A detective story in the purest sense of the word and the most conventional one from these two volumes.

The next story, "Another World,' brings Sou and Kana to New Jersey. Two years previously, a mathematician working on proving the Riemann Hypothesis, Professor Kenneth Refla, invited to Sou to return in two years to witnessing him unveiling the solution. And making history in the process. Those two years have come and gone, Sou returned to New Jersey to witness this great event. Sou tries to explain explain this "famous conjecture which no one has been able to prove for 150 years" to Kana ("Ha, I didn't under a single word"), but it boils down to "if the Riemann Hypothesis can be proven, a connection between the real and abstract world of prime numbers can be established." But, when they arrive, they're told that the presentation has been canceled months ago. Professor Kenneth Refla has simply disappeared from the face of Earth. So what happened? But left behind a number of clues.

Firstly, a quatrain, a poem with four lines, is found stuck to the window of his home office. Secondly, he distributed four paintings depicting lines from the quatrain. Thirdly, a coded tombstone. However, "Another World" is not, strictly speaking, a traditional mystery, but one of those really strange, character-driven and surprisingly humanistic mathematical puzzles you can only find in this series – reminiscent of "The Frozen Hammer" (vol. 9) and "Dedekind Cut" (vol. 15). Just not nearly as effective or poignant as previous attempts at such stories. Although I liked that brief moment towards the end between Sou and Kana ("don't worry, I won't go over to that side"). So a nice little bit of storytelling, but, on a whole, not the best or most memorable entry in the series.

I really should have planned out these reviews, because vol. 24 opens with a seasonal-themed mystery, "Christmas Eve Eve," which is appropriately a very minor mystery with an even slighter plot. Sou and Kana take a part-time job together at a karaoke bar to earn some extra pocket money to buy presents. What they end up doing is playing Santa's Little Helpers by clearing up some minor crimes and misunderstandings among the other employees of the karaoke bar ranging from a possibly stolen wallet to a potentially cheating boyfriend. A nicely-done, but really threadbare, detective story that I've nothing to say about at the moment. I might return to it in December and review it separately as it probably works slightly better when you're in the Christmas spirit. Only time will tell.

The second and last story, "Crime and Punishment," is a quasi-inverted mystery with a ultimately simplistic, but delicious, twist ending.

Kunihiko Sendagawa, a post-grad student, is struggling to make ends meet and "a mountain of debt bills" on his doormat keeps growing. That eats at his mind. After all, why does someone as smart as him needs to struggle for money? But he gets an idea when he learns a serial burglar is active in neighborhood. So he decides to start burglarizing houses beginning with his own place in order to divert suspicion ("the police wouldn't suspect a previous victim like me"), but, on his second job, Sendagawa finds the body of an elderly man – brutally beaten to death with a golf club. Unfortunately, for him, the policeman on the case is Kana Mizuhara's father and Inspector Mizuhara is no Lestrade. While he initially thinks "the serial burglary case has finally escalated to burglary and murder," Inspector Mizuhara begins to notice inconsistencies in Sendagawa's statements and takes note of his outright suspicious behavior. So decides to start playing Columbo with the post-grad student ("it's so annoying to be followed like that"). Sendagawa turns in desperation to Sou and Kana to help him out of his current predicament, but Sou tells him Inspector Mizuhara wouldn't suspect a person without a reason and advises him to simply confess whatever he has one his conscience.

Sendagawa naturally ignores Sou's advise and digs an even deeper hole for himself, which eventually brings him back into the case to go over "the distorted hints" that explain who killed the old man and stole the money. I should have seen it coming, but, somehow, completely missed and wanted to kick myself for not immediately figuring out a very basic, tell-all clue (SPOILER/ROT13: “V qvqa'g xvyy gung Fnagn Pynhf-yvxr byq zna!”). A low-key great story and fun to see Inspector Mizuhara getting to enjoy the spotlight for a few fun scenes!

So, all in all, two very solid, highly enjoyable volumes as vol. 23 opened strongly with a cleverly plotted, simon-pure jigsaw-puzzle detective and vol. 24 ended on a high note with an excellent treatment of the inverted mystery. The two stories sandwiched in between are of middling at best, but nothing to the detriment of the overall quality readers have come to expect from this series. More importantly, they demonstrate why Q.E.D. has become a personal favorite of mine. The series will never beat Case Closed as my favorite manga mystery series, but Q.E.D. will be equally hard to wrench from its second place spot. As always, to be continued!