It's when Tani went to where Irisu's character was in hiding -- something to do with knowing something that could bring down Yuumi Hiro's evil plot, I think, which he abetted because he needed money for his sick daughter -- and Tani beat some sense into him in front of his wife.

I really want to watch it again so that I can figure out all the sub-plots.... God, I love Masatsuka-sensei's shows♥