The Streets of San Francisco

The Most Deadly Species (3x2)

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When a high-ranking hoodlum's son is found murdered he brings in the help of the adrogynously named "Sydney"--a hit woman who's assigned to murder the three thugs responsible. Stone an Keller are looking for them, too. Somehow Sydney becomes Keller's next door neighbor and a relationship develops during their investigation. When Stone & Keller discover two of the hoodlums have died before they can be brought into custody, Stone suspects the worse: his partner is sleeping with the killer. Sydney is played by Brenda Vaccaro, who at the time was married to Michael Douglas.