Sherlock and Joan investigate the scene of a fire and realize that the vicim was clearly murdered.
The investigation reveals that the victim was attempting to locate some notoriously-bad console games that had been intentially buries in landfil. They learn that he was getting help from an online mentor of sorts.
The "mentor" turns out to have been laeading the man on, and had no intention of leading the archaeologist to the real site of the cartridges, which was actually his backyard shed - he'd had them for six years.
They discover then that the archaeologist had found toxic chemical barrels. He went to the landowner, who may be held liable, either to notify him or extort him. Whatever his goal, the landowner had an arsonist kill him and attempt to make it look like suicide, which ultimately didn't work.
Meanwhile, Sherlock's former sponsor Alfredo returns from an extended stay with his siter out of state. He seems eager to reconnect with Sherlock, and it soon becomes apparent that he is struggling emotionally, for reason he can't even begin to articulate.
Sherlock connects with Alfredo and offers to listen to his problems, a major step forward in his evolution as a person.