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…