Watson is asked by an old friend to track down the man she had a one night stand with a year ago. When Joan almost finds out who it is, Sherlock confesses it was him. He also reveals that he used to follow around because he didn't trust her when they first met. Joan dreads telling her friend that her partner is her mystery man but Sherlock goes to tell her himself when he sleeps with her again.
Sherlock and Joan are taken through a case when an assassin is killed. They are taken through a loan shark, the Russian Mafia, and finally back to the doting wife was scorned by her assassin husband.