Maynila sa mga Kuko ng Liwanag (1975) follows the allegorical tale of Julio Madiaga, a naive boy from the province, who comes to the city of Manila in search of his long-lost lover, Ligaya Paraiso, who previously came into the city in search of a good life. Julio's views about a dreamy Manila that promises good life and success are immediately crushed when he himself has to contend with the pressures of living in the city: the need to meet one's daily subsistence and likewise the struggle to survive. In search of Ligaya, Julio discovers the city's own underbelly, hidden from plain sight, which is another nod to Manila's underneath filth amidst all that dreamy vibrance, like how dirt under one's nails can only be seen before a source of light.

At the start of the film, Julio passes by the corner of Ongpin and Misericordia, and will pass by such area from time to time later on, for he suspects that Ligaya, his lover, is somewhere in that peculiar building from across such corner. In his pursuit of Ligaya's whereabouts, Julio first lands a job at a construction company, where he befriends a local, Atong, who tells him about life in the city. Julio begins to realize that the only way to truly enjoy urban comfort is when one has sufficient income to last him a lifetime. Only a few days pass when Julio also learns about the Taywan system, a payment system by their middle-class bosses that exploits the working class; the accidental death of his co-worker Benny who, like him, also hails from the province; and the poor, urban life in Manila's slums, specifically, when he escorts Atong to the latter's house and meets the latter's family: Atong's wife, Perla, and his sickly, bedridden father.

Meanwhile, throughout the film, Julio has chance encounters with Mrs. Cruz, a fat lady dressed in black who previously escorted Ligaya into the city and promised her education and work. In two of those instances, Julio was able to catch up and confront her, yet the screaming lady purposely accused him of being a street burglar; leading Julio to cede from his actions.

When Julio gets removed from work along with other displaced workers, he takes in the aid of Bobby, a callboy who guides him into the world of male prostitution. There, he sells his body for cash and discovers the reality of underground male brothels that are no different from Manila's underground sex dens and female prostitution rings; a reality that reveals the city's very own underbelly.

Later on, Julio reconnects with Pol, a colleague of his in one of his previous job occupations in the city. Together, they learn about Atong's untimely death at the hands of the ruling clique, Atong's area of settlement burning down to ashes, and Perla's alleged abduction. When Julio finally reunites with Ligaya, the latter tells him of her life in the city: how Mrs. Cruz lied to her about affording her good education and work; how Julio was right in his suspicions about the peculiar building from across the corner of Ongpin and Misericordia; how she was forced to become a prostitute and a kept woman for Ah-Tek, an unscrupulous mestizo de sangley; and how she was pregnant with her and Ah-Tek's four months old baby. Emotions become apparent on screen: Ligaya's full-blown emotional meltdown, in her unbecoming of a happy, beautiful woman, and Julio's rage, in his confrontation with the utter reality of city life and in his shedding away of naivety and innocence from being a mere province boy (probinsyano). Together, they plan their return to Marinduque, their home province.

This plan would not come into fruition, however, when in the film's last few minutes, Pol informs Julio of Ligaya's death. She is told to have allegedly fallen down the stairs, yet the apparent bruising on her body says otherwise. Enraged, Julio stabs Ah-Tek with a kitchen knife, ultimately killing the latter, and flees away, with an angry mob of city dwellers following him across Manila's slums. The film ends with Julio having to face his implied death at the hands of his very own people.