Finally. This is the turning point of the career of the Shinsengumi. The essentials of what happened are covered in RK #93 and in one of the Flashbacks in the current chapter, if I'm not mistaken. (I've seen only the translations and not the mangas.) I'm just adding that most of the killed Shishis are from Choshu and Tosa. It was after this affair that the Shinsengumi became national heroes overnight. However, the affair costed Okita a heavier price than anyone bargained for... (see section on Okita for more info)