Fire elements Bernie and Cinder Lumen embark on a journey as they immigrate from Fire Land to Element City, only to confront the challenges of xenophobia from other elemental beings. Their story takes a turn with the birth of their daughter Ember, for whom they establish their own traditional outlet, the Fireplace, embodying their heritage with their signature Blue Flame. However, as time passes and Bernie expresses his desire to retire, he has one condition: Ember must learn to manage her fiery temperament before she can take over the store.
One fateful day, as Ember attempts to handle the store alone, she becomes overwhelmed by the crowd and retreats to the basement. In a moment of frustration, her fiery outburst inadvertently breaks a water pipe, leading to a flood and the unexpected arrival of Wade Ripple, a water element and city inspector. Despite her protests, Wade must report the plumbing issues, which puts the Fireplace at risk of closure due to the findings he must submit to his boss, Gale Cumulus, an air element.
Wade, however, strives to help Ember save her father’s shop and takes her to Cyclone Stadium to discuss her store’s future with Gale. During this meeting, Wade reveals that he had been tracing leaks in the city’s canals and proposes a solution: if they can address the source of the leak at the Fireplace, perhaps Gale would reverse the decision to shut it down. They work together, and soon discover a gap in a dam that allows water runoff to disrupt the city’s plumbing. Combining their efforts, Ember and Wade close the gap, leading to a blossoming connection between them as they spend time exploring Element City.
Returning to the fire plant, Cinder grows suspicious of her daughter's interactions with Wade. Eventually, when the sandbags they used to seal the hole fail, Ember ingeniously melts the sand into glass for a more resilient patch. During a visit to Wade's luxury apartment, she uses her talents to fix a broken glass pitcher, which impresses Brook, Wade's mother, who encourages her to pursue a glassmaking internship.
Their emotional bond deepens as Wade, while playing "the Crying Game," confesses his feelings for Ember, causing her to shed tears. Just then, Gale approves the solution to the plumbing issue, allowing The Fireplace to stay afloat. However, with her father’s retirement announcement looming, Ember realizes that she does not want the burden of running the store.
In a tender moment, Wade reveals Vivisteria flowers to Ember, showcasing their remarkable ability to thrive in diverse environments, a sight she yearned to witness in her youth. The experience is magical, yet it stirs conflict within Ember, caught between her love for Wade and her familial duties, leading her to end their relationship despite Cinder sensing their undeniable connection.
Amid escalating tensions, Bernie's plans to pass on the store crumbles as the Fire district faces further flooding, ultimately leading to a moment of peril where Ember and Wade find themselves trapped in the Fireplace. The heat brings Wade to evaporate, amplifying Ember's grief as she comes to terms with her feelings for him. She then devises a way to restore him by playing the Crying Game, effectively bringing him back to life physically, culminating in their first kiss.
In the months that follow, with Bernie comfortably retired, friends now operate the Fireplace. Ember and Wade, transformed as a couple, set off on a new adventure, leaving Element City behind as Ember steps into her dream of pursuing a glassmaking internship.
