Who Killed Mary Whats'ername?

In New York City's Greenwich Village, a prostitute named Mary Di Napoli is murdered. A few days later, diabetic, fifty-something ex-prizefighter Mickey Isadore is released from the hospital and warned by his friend and physician, Dr. Barkunian, to alter his lifestyle. Mickey has seen the small newspaper item recounting Mary's death and, appalled that no one seems to care about the woman or who killed her, determines to investigate himself. Seeing his daughter, Della Longo, in the hospital hallway and knowing she will object to his plan, Mickey evades her by taking a cab to Mary's apartment. There, he rents her empty rooms from the neighbor, Malthus, an unfriendly hippie who states that Mary was "infested with sin." While inspecting the apartment building, Mickey climbs the outside fire escape to her back window, attracting the suspicions of Officer Solomon, who warns him to leave. Mickey then goes to the local bar, where bartender Larry informs him that Mary visited the night she died, wearing fancy clothes in order to appear in a film a local man was shooting. Spotting another prostitute, Christine, across the street, Mickey decides to follow her and so enters a diner near her street corner. When Christine comes in to order coffee, two bikers, Whitey and Joe, and their female friend pursue her. The men begin to terrorize Christine, threatening to beat her up, until Mickey warns them to stop. Assuming the older man will be easy to subdue, the bikers attack him, but are severely beaten. Just as Joe pulls out a switchblade, a police siren sounds nearby, and the bikers run off. Mickey walks Christine home, questioning her about the bikers and the filmmaker. Christine, who professes not to know the bikers, tells Mickey about the man, Alex Monteliagra, who is making a documentary about prostitutes. She invites Mickey to her room, which is in the same building as Mary's, and offers him free sex, but he politely declines. Back at Larry's, Mickey tries to question the other prostitutes there, but receiving no answers, instead befriends Val Rooney, an out-of-work insurance salesman who has been drinking too much. As the two leave the bar together hours later, Val recognizes Mickey as a former champ. Mickey explains that he is looking for Mary's killer because he, too, grew up in a squalid neighborhood and could easily have ended up like her. Just then, Whitey and Joe appear and try to run Mickey down with their bikes, but after a close escape, the police show up and chase off the bikers. Mickey then goes to his well-appointed home, where he lives with Della. When he describes to her the events of his day, she asks him to give up the chase and protect his health, but when he refuses, she is proud of his determination. The next morning, when Mickey leaves to find Alex, Della insists on joining him, as does Val. The three find Alex, who slams the door on them, until Della returns alone and gently asks to talk to him. As the two converse, Mickey and Val return to Larry's and learn that the girl with Whitey and Joe was Angela, Mary's estranged daughter. Della soon summons them to see Alex's footage, which shows Mary on the night of her death. Noting that the last man seen with her wears horn-rimmed glasses, Mickey asks Christine about the man's identity. Although she is reluctant to recall that night, she reveals that the sinister man calls himself Capt. Marvel, and one night received a parking ticket from Solomon. After persuading Solomon to give him Capt. Marvel's license plate number, Mickey tracks down the man's real name, Roger Boulting, and work phone number. Della then calls Boulting pretending to be a young prostitute whom he has impregnated, and makes a date to meet him. That night, Alex sneaks Della into a movie theater, but disappointed with the focus, insists on talking to the projectionist. Meanwhile, Mickey grows concerned for Della and searches for her, finally discovering her at home with Alex, whose apartment has just been ransacked and his film equipment burned. Mickey offers Alex the use of their spare room. The next day, Mickey and Della meet Boulting, whose obnoxious leering, disregard for Della's "condition" and insistence that he does not know Mary prompts Mickey to punch him. Later, Della calls Mickey to inform him that she and Alex have rented a motorcycle and are following the gang to keep tabs on Angela. Despite Mickey's concerns, they return that night unharmed. When Mickey requests to see the rest of Alex's film, the young man secretly hides one canister of footage. The next day, Mickey, Della and Val return to the warehouse where the bikers live. Mickey approaches Angela, but just then Whitey enters and Angela runs away. While Mickey chases Angela up to the roof, Whitey follows and grabs Mickey, who escapes only by stabbing him with his insulin needle. Back at home, Mickey looks through more of Alex's footage, and later asks Della if Alex left her at all the night of the fire, thus providing an interval in which he could have set it himself in order to destroy some of the film. Reluctantly, she admits that he was with the movie projectionist for twenty minutes. Later at a bar, Christine informs Mickey that Mary had fallen in love, but she cannot recall the man's name. Outside, Mickey sees Malthus and several elderly women enter a building, and there finds Alex secretly filming as Malthus preaches to a prostitute that she is defiled. While the ladies watch approvingly, Malthus grabs the prostitute roughly, prompting Mickey, who is disgusted with Alex's inaction, to grab the woman and pull her away. Val accompanies Mickey to visit Leo, a former client of Mary's whom Christine has remembered. At the rest home in which he lives, Leo informs them that Mary wanted to stop working after she fell in love. On the way home, Mickey reveals to Val that he cannot become overtired, as it may cause him to go into a diabetic coma. Mickey returns to Mary's apartment, where Christine enters and soon falls asleep on his bed. Knowing she has left a note on her door informing her clients that she is at Mickey's apartment, he leaves her there with the door unlocked. At home, Mickey demands to see more of Alex's footage, and there discovers that the woman shown with Boulting is not Mary but Angela. When Mickey returns to Mary's, Solomon, who still suspects him, stops him outside and reveals that Malthus is a drug addict who cons the old women into paying him to "reform" prostitutes. Inside, Mickey discovers Christine's dead body. Blaming himself for putting her at risk, he decides not to inform the police yet, and instead instructs Della to spread the word that Christine has survived. Back on the street, he sees Alex following the old women into an alley, where they have surrounded Angela and are assaulting her. Mickey rescues Angela, who then tells him that on the night of Mary's death, she brought Boulting to her mother's apartment and discovered her murdered body there. Meanwhile, Della has looked through Alex's film and found the hidden canister, which shows Alex finding and filming Mary's dead body. Mickey feels himself beginning to go into a diabetic incident, but cannot locate any candy to help maintain his blood sugar. After warning Della to avoid Alex, he heads to Christine's apartment, hoping that the killer will hear that she has survived and return there to finish the job. At Christine's, a desperately weakened Mickey struggles to stay conscious and remembers Christine. Hearing footsteps, he is unable to rise even when he sees that the intruder is Val. Val confesses that Mary fell in love with him and threatened to tell his wife, then told Christine about him, compelling him to kill them both. Mickey passes out, and certain he will soon die, Val leaves him. Just then, however, Della arrives with the police, in time to arrest Val and rescue Mickey.