Matt Hagen is a rising, vain film actor starring in pulp crime movies on the Gotham City studio lots. Desperate to break out into prestige cinema, Hagen gets entangled with mob-backed studio executive Anthony Delane and loan shark Roland Daggett. When Hagen refuses to sign an abusive contract that forces him to launder dirty cartel money through his upcoming film productions, Daggett’s henchmen ambush Hagen inside his dressing room, brutally beating him and forcing his face onto a hot iron grill, permanently disfiguring his features.

Mutilated and abandoned by his agents, Hagen retreats into total isolation. Desperate to salvage his career, he approaches Dr. Sarah Charles, a biochemist conducting covert clinical trials with "Renu", an experimental regenerative biopolymer capable of restructuring damaged human tissue. Sarah warns Hagen that the chemical compound remains untested on human skin, but Hagen steals the serum and injects it directly into his facial muscles.

The results are miraculous: Hagen's burns vanish, and his flesh becomes pliable enough that he can manually sculpt his jawline and cheekbones back to perfection. Ecstatic, Hagen returns to the studio and secures his dream role. However, the formula quickly proves addictive and unstable. The effects wear off after hours, forcing Hagen to inject higher doses. During an audition, Hagen's cheek begins to melt, sliding off his face under the hot studio lights before he flees in panic.

Hagen breaks into Sarah's research facility to steal the remaining stockpiles of Renu. Daggett’s enforcers track him to the lab, hoping to steal the chemical for commercial cosmetic black-markets. During a violent struggle, the enforcers douse Hagen in a vat of concentrated chemical mutagen and dump his body in a drainage pit on the industrial outskirts of Gotham.

Instead of dying, Hagen's entire cellular matrix breaks down and reconstitutes into an amorphous, sentient mass of malleable protoplasm. Retaining his memories and burning with rage, Hagen learns to mold his mass into human disguises. He infiltrates Delane’s mansion, shifting into the likeness of Delane’s business partner, before suffocating the producer by forcing malleable clay down his throat. As his mind fractures under the weight of his shifting cellular identity, Hagen launches a bloody crusade against every individual responsible for stealing his face.

Hagen's vendetta culminates on the opening night premiere of his unfinished film at the Gotham Royal Theater. Disguised as Daggett's bodyguard, Hagen corners Daggett inside the private projection booth. Sarah arrives with an experimental chemical neutralizer, begging Hagen to remember who he was and step away from vengeance.

Hagen breaks down, his voice shifting erratically between multiple people he has impersonated. Looking at the movie screen projecting his former handsome face, Hagen weeps, stating that Matt Hagen was always just an empty mask. As police surround the theater, Daggett pulls a gun, shooting Sarah in the shoulder. Enraged, Hagen sheds his human disguise completely, transforming into a colossal, weeping clay behemoth that crushes Daggett against the theater screen.

When tactical police open fire, Hagen shields Sarah from the gunfire. To save her life, Hagen hurls himself out the high stained-glass window into Gotham's rushing drainage river below.

Weeks later, Sarah is recovering in a medical clinic, continuing her regenerative research safely. In the final scene, a street-performer in a crowded Gotham plaza is seen twisting clay sculptures for children. A young boy asks how he makes the faces look so real. The man turns around, his jawline subtly shifting and blending like wet dough, smirking before disappearing into the foggy city shadows.