Detective Bell considers leaving the NYPD when he is recommended for a once-in-a-lifetime career opportunity. Also, Holmes and Watson are hired by a private client to investigate the disappearance of a young woman who led a double life online as a financial dominatrix.

Holmes and Watson race to help Detective Bell when he becomes a victim of a bio-terrorism attack at the precinct and the station is quarantined. During the lockdown, Captain Gregson and Detective Bell begin to suspect they are trapped inside with the perpetrator. Also, Watson faces the difficult task of helping her mother, Mary, accept that her advancing Alzheimer's disease requires her to receive more medical care.