7. The Marchioness

Complete story — includes the ending

Mycroft is opening a new restaurant named Diogenes in New York City. Sherlock had slept with Mycroft's ex-fiancée, Nigella Mason, to prove to Mycroft that she was after his money. Instead of marrying Mycroft, Nigella landed a marquess. She had an affair with her stablemaster, which led to divorce. She fought hard to get Silver Blaze, a retired champion racehorse, as part of the settlement. The stablemaster is killed by someone trying to poison Silver Blaze. Nigella is charging $100,000 stud fees for Silver Blaze's services. Sherlock proves that the horse died of natural causes, so Nigella substituted his lookalike brother. One of her clients, however, was Joaquin Aguilar, the head of a drug cartel; he found out and sought revenge using a hitman. Sherlock sets a trap for the hitman and catches him. Sherlock and Mycroft promise not to turn her in as long as she pays back her victims, with the exception of Aguilar. Sherlock threatens to reveal that Aguilar sold his foal to another unsuspecting horse lover, unless Aguilar stops seeking revenge. It is eventually revealed that Joan and Mycroft slept together when they were in London and have not since talked about it.