Episode 4 of On Call kicks off with a poignant memorial service for Maria Delgado, leaving Harmon in a state of tears, overwhelmed by grief. She subsequently takes Diaz to her beloved food stall, run by a friendly chap named Chad. Their bond stems from an incident where Harmon caught a thief who had robbed Chad, earning her free meals as a gesture of gratitude. As they revel in their culinary delights, a call interrupts their peaceful repast, alerting them to a disturbance.
Rushing to a motel, they are greeted by the sounds of a heated altercation between a man and a woman confined within one of the rooms. Upon entering, they discover a prostitute claiming to have been brutalized by the man, while he counter-accuses her of scalding his genitals with boiling water. In an attempt to extricate himself from trouble, the man spills the beans to Harmon about East Barrio members who had been at the hotel the preceding night, discussing the delivery of a significant package.
Harmon proceeds to interview the woman privately, who confesses that one of her prostitutes, Baby Blue, had been in the company of the East Barrio men. Locating Baby Blue, Harmon extends an olive branch, promising her assistance whenever needed, in exchange for information. Baby Blue divulges that Maniac was indeed present the night before and had invited her to the Oceanside Motel the following evening, an invitation she declined.
That night, they set up surveillance at the motel and spot a car registered to an East Barrio affiliate. Although Harmon expresses concern about Diaz's lingering doubts in her judgment, he reassures her of his unwavering trust. Harmon inquiries at the motel's front desk and learns that four individuals are occupying Room 112, leading her to believe that Maniac is among them. They request additional backup, including Sergeant Lasman.
The officers storm the room but find it deserted, save for a young girl hiding in the bathroom. Suddenly, bullets spray into the room from the adjacent suite. The officers spring into action, neutralizing the threats in the neighboring room, but Maniac slips through their fingers. Harmon hotly pursues him to an abandoned building, where a fierce confrontation unfolds. In the midst of the scuffle, her body camera detaches from her uniform. She manages to point a gun at Maniac's temple, momentarily contemplating pulling the trigger. However, Lasman intervenes, seizing Maniac.
Later, Harmon dispatches the young girl they discovered to an ambulance, while Koyama arrives to offer her both commendation and solace. Back at the precinct, Bush grills Harmon on how she deduced Maniac's presence at the motel. She emphasizes that if Harmon deviated from procedure, he must be informed.
As the day draws to a close, Lasman inquiries of Harmon if she has ever entertained the thought of shooting Maniac. She shakes her head, a firm negative. Meanwhile, Diaz prepares to venture out for a night of revelry with his fellow officers, and Harmon, in agreement, promises to join them shortly. Once Diaz departs, her gaze drifts to a photograph of Delgado, and the weight of her emotions bears down upon her, culminating in a heartfelt breakdown, bringing Episode 4 of "On Call" to a poignant close.
