George Nix is killed, for real, at a Revolutionary War re-enactment. Nix's bodyguard said Nix had received death threats from franchisees in his gym chain. Sherlock tells Dr. Hanson his headaches are getting worse. He prescribes a higher dose of painkiller. Sherlock rules out those sending hate emails to Nix. He does turn up a suspect, Nix's estranged daughter Marcy. Marcy tells Joan and Marcus that she won't touch her $5 million inheritance and will give it away. Gregson calls to tell them someone burned down Nix's house. Joan suggests Nix's collection of Paul Revere silver was stolen before the fire was set. Joan and Sherlock go to see Detective Mason, who holds a grudge against Sherlock from an earlier case they worked together. He agrees to assist them if Sherlock helps him with another case. Sherlock solves that in about 30 seconds looking at a stack of crime-scene photos. A fire chief stole the items, but wasn't involved with the murder or the arson. Sherlock deduces that the documents inside the fireproof safe were the arsonist's target. He uses an old British solution to restore the documents. Nix was trying to corner the market on autographs by Button Gwinnett, a signatory of the Declaration of Independence, and these were in the safe. Someone with other Gwinnett signatures would benefit. They bring in Paul Chambers, who has some. But he points out he was trying to buy Nix's collection. Joan discovers one of the burnt documents affects a modern case, in which descendants of a Revolutionary War soldier are trying to reclaim his land from a New York developer, Chris Holland, also a re-enactor. Holland's litter box revealed traces of substances used to set the fire, and he confesses. MIchael asks Sherlock to track a missing woman from AA.