Sherlock and Joan investigate the death of a base jumper who was shot by a sniper in mid air, but Sherlock discovers that the straps on his parachute had been cut and he would have died regardless. They initially suspect the wife, his base jumping partner and a colleague from his time as a military contractor. The deceased had received a large sum of money, which Joan and Sherlock thought was the result of blackmail, but turned out to be an off the books loan, used for the purchase of a plane. After examining the plane Sherlock finds seats in the cargo hold, and they realize the plane is used to illegally smuggle immigrants into the country. During questioning of the wife she admits to cutting the straps on the parachute, because her husband had been having an affair, but she had changed her mind and begged him not to jump. After interviewing two of the immigrants smuggled on the plane they realize their daughter is most likely the woman who had been having an affair with the deceased. Their son had been associated with the Taliban, and in his belief system premarital sex was a great dishonor to their family. He had killed his sister's lover and planned to kill his sister, but the police captured him in time.
In the secondary story Joan's sister, Lin Wen, tells Joan that she saw a man she thought was a gang member talking to Shinwell Johnson, Joan is worried because it might effect Shinwell's parole. Through police photos Lin identifies the man as Tall Boy, a former gang associate of Shinwell's and member of SPK. When Joan confronts Tall Boy he tells her that Shinwell contacted him. Sherlock meets Shinwell in park where they play chess and Sherlock warns Shinwell not throw away his opportunity to change. At the end of the episode Shinwell tells Joan he doesn't want her help anymore and threatens her.