Rough and tumble SFPD Inspector Johnny O'Rorke, the department’s Executive Protection Officer, has a new partner, Cosmo the Wonder Dog, a Lakeland terrier his sister has left in his care.

O'Rorke is called to San Francisco City Hall to meet with Film Commissioner Audrey Pebble. Warner Brothers is preparing to film a major motion picture, Dirty Harry, in San Francisco, with Frank Sinatra set for the starring role as Inspector Harry Callahan.

Pebble knows that O'Rorke has worked as a bodyguard for Sinatra. She hired Harly Walker, a local young artist and musician, to scout the city for locations that would appeal to Warner Brothers. Walker has disappeared and Pebble is desperate for O'Rorke to find him.

The hunt takes O'Rorke and Cosmo to the famed Haight Ashbury Medical Clinic and to some of the darkest, most dangerous areas of the city, including porno movie studios, drug dens, bathhouses and hardcore leather bars.

While searching for Walker, O'Rorke learns that several of Harly’s friends have been murdered in such a painful manner that even the medical examiner is shocked.

O'Rorke races to find the killer–and then comes the hard part: Telling Frank Sinatra that he is not right for the role of Dirty Harry.