The "O'Brien" of the title is Mrs. O'Brien (Lillian Bronson), the feisty old manager of the apartment building wherein resides Officer Pete Malloy (Martin Milner). Someone has stolen Mrs. O'Brien's purse, and she is determined that the police capture the thief--even if it means picketing the Rampart station, much to Pete's annoyance and embarrassment. This episode was originally scheduled to air on November 2, 1972. ~ Hal Erickson, Rovi