Go with the Plan: Q.E.D. iff vol. 3-4 by Motohiro Katou

The first, of two, stories making up Motohiro Katou's Q.E.D. iff vol. 3, "Three Killers," concern three women, Kurotsu Yui, Okada Miki and Fujishima Akiko, who have all fallen victim to Yamaguchi Senji – president of a predatory investment company ("let them try and sue me"). They all three lost much more than just money giving them a pretty strong motive to murder him. Only for an opportunity to presents itself.

Yamaguchi Senji's company holds and manages art pieces for investment, but clients rarely get their money or art pieces back. So the company has build up a modest stock of art pieces and intends to auction them off during a special gathering at his lavish mansion, which he pitches as "if everybody were to buy art works at high prices" then "the market price would also increase" and everybody profits. Yamaguchi Senji intends to make an absolute killing by emptying out their stock, but the three women plan to make a killing of their own. But here's the kicker. They're working independently from each other, not in tandem, who come each with a plan of their own that collide head on the moment they're put in motion. So, needless to say, the result is a beautiful and confusing mess.

Sou Touma and Kana Mizuhara were asked to try and get back a dish the company took to be invested, but never paid out or returned the dish. They also happened to be there when Yamaguchi Senji met his strange, violent end Touma offers a solution in return for the dish. Touma's explanation of the chain of events from that evening is quite impressive from the blood soaked bed, a dead snake in the trash and a dented vase to an empty, thoroughly searched room – only stretching it when it came to how the body ended up in the pool. Other than that, "Three Killers" is a mostly very well done inverted mystery taking The Trouble with Harry approach to murder.

The second story from Q.E.D. iff vol. 3, "The Bike Thief," begins as a fairly minor character-piece, centering on a six-year-old incident, when Sou Touma briefly returned to Japan from America over the summer holiday. An even younger Touma was weeding a garden as a summer job when coming across a brand new bike in the tall grass with a price tag on it. The bike was reported stolen from a shop and the local policeman believes Touma pretended to find the bike he stole himself, because a witness claimed a child cycled away on it. Touma denies it and the incident remained unresolved, until Touma returned to the village to witness an old house being demolished. So meeting the people from back then again brings up the old incident and honestly didn't expect too much from this story, except coming up with a creative reason to steal and dump a brand new bike. That it delivered. It also had an unexpected good method to steal a bike. On a whole, "The Bike Thief" turned out to be a much more involved detective story than its opening suggested and solid closer to this volume.

The first, of two, stories from Q.E.D. iff vol. 4, "The Jade Miko," really should have been a volume-length story. The backdrop is Indigo Island, ruled over by the Yuna clan, where a small community have lived generations by farming and fishing. Now the community is being ripped apart over plans from a Tokyo developer to turn the island into a holiday destination by building a resort, but the plans face opposition from half the islanders. A situation hardly improved by the disappearance of the company's surveyor and gets even worse Yuna Aoi, head of the Yuna clan, "divined that the body was buried on another island." She "divined perfectly" where the body was buried, but that only made her suspect in the eyes of the police. Fortunately, Yuna Aoi's younger sister, Shiomi, is a friend of Kana Mizuhara and they entice Touma to come to Indigo Island to sort the case out. What they find on the island is not merely a dispute over a development project that ended in murder, but a murder tied to the history and mythology of the Yuna clan and island. There is, of course, talk of an old curse that has struck down people before and apparently continues as two more murders follow. Two seemingly impossible murders!

First of these two impossible murders begins, similarly to the first murder, with a disappearance. This time, it's the company's lawyer who goes missing and during the subsequent search a cave is inspected, before high tide, but is found to be empty – only for a second search to reveal the body. So how did the murderer get the body inside the cave when it was under water? I had a pretty good idea how this trick was done, but not the second one. And that one takes the prize! A body is found nailed with a knife to the sacred tree on the beach, but "there are no footprints on the sand" anywhere near the crime scene. Funnily enough, I recently mentioned in my review James Scott Byrnside's "Red River" from The Architecture of Murder (2025) how difficult and tricky the no-footprints scenario is to pull off successfully and satisfyingly. Even more difficult to achieve with the no-footprints problem is being original. Byrnside ticked all the boxes with "Red River" as I can't recall having come across anything similar, but Katou definitely came up with a new solution here. I'm truly surprised nobody has come up with it before! In a way, it's the easiest and maybe even the most logical way to do it.

"The Jade Miko" is solid story overall hampered only by the fact that it should have been volume-length story, because the plot needed more space and getting rid of the next story would be no great loss to the series.

I've barely anything to say about the second and last story, "H.N. (Handle Name)," which somehow feels oddly out of date. A story that could have been published in the early or mid-2000s. Sou Touma helps out a cyber security expert, Matt Brown, who stopped an online casino from being hacked and now he's being targeted by the elite hacker known as Crash. But this story is more cringe than anything else. So not a great story to end this volume, or review, on, but not a bad haul altogether. "The Jade Miko" is the highlight of these two volumes, closely followed by "Three Killers" and "The Bike Thief" developed into something interesting towards the end. Only "H.N. (Handle Name)" was bad, surprisingly bad. Well, three out of four ain't bad.

Next manga mystery review is going to be either Case Closed or C.M.B.