While in his isolation chamber, Sherlock dreams about being at Captain Gregson's graveside. When he emerges, he finds a text from Joan that Gregson has woken up. Sherlock and Gregson make up. A panel van crashes into a semi at a traffic light, then explodes. The gasoline truck bomb kills the van's driver and a nurse trying to help. Marcus thinks it might be terrorists, whereas Sherlock thinks it's a Salvadoran gang. Gregson tells Joan that Patrick Mears lied about their timeline. Sherlock discovers that former gang leader Halcon is now a Connecticut youth soccer coach. Halcon (now Danny) finds out that the van was a fuel skimmer stealing gasoline. Sherlock thinks the light was either broken or hijacked. Sherlock accuses a federal gang task force of staging the crash. After their reaction, he rules them out. While most were incensed, FBI Agent Tanyag said a hacker named Overlord had put a virus inside the traffic grid. Joan says Mears is protecting an accomplice. Joan interrogates Mears, who explodes when she calls him a terrorist. NSA Agent Heller and Overlord, aka Phil, who is now working for the NSA, show up at Sherlock's door. Phil determines that other lights had been hacked but Sherlock decides that the truck was the target. Jarius the driver didn't know what his cargo was. It was elevators, according to construction-company owner Dewashe. The resulting delay might have kept him from his next multi-billion-dollar project. The next highest bidder on that job was Maranek Construction. But Saul Maranek-Halevi, the likely hacker, is gunned down by two gang members. A co-conspirator had arranged for him to be killed. Saul's father-in-law has a mole inside Dewashe's company slowing down his projects and she gives him up. Mears' wife Tina confirms he communicated through the video game chatroom.