Rookie detective Yu Lin took over the first gas poisoning case. Shu Qin, the wife of the deceased Wang Wei, was extremely calm and had a perfect alibi. The case was initially determined to be an accident. Yu Lin had doubts. When he was seconded to Dong County, he discovered a highly similar gas explosion case. Qu Yao, the wife of the deceased Zhang Lei, also left home at the time of the crime and had an impeccable alibi. In both cases, the expired gas hose "accidentally" fell off. Both wives had murderous motives. They left home on the same day and the crime occurred on the seventh day. Yu Lin boldly deduced that it was a cross homicide. After verification, Shu Qin and Qu Yao had already met at the domestic violence help center. The two hired rider Lin Xiao and terminally ill Wu Pinde to join forces to commit the crime.
