Joan discovers an unsolved murder connected to a rare prehistoric fossil when she reviews one of Sherlock's cold cases; Sherlock's responsibilities as a sobriety sponsor cross personal boundaries.

Holmes and Watson retrace Holmes' steps after Holmes finds himself in possession of a severed head and can't remember anything about the last six hours.

Holmes takes extreme measures to secure his return to New York when he leans on his father’s disreputable connections to aid his legal re-entry into the United States. Also, while Holmes looks for a way back to the United States, Watson helps the NYPD investigate a murder at a storage facility that caters to wealthy clients with items they want hidden from U.S. Customs.