Fire elements Bernie and Cinder Lumen immigrate to Element City where they face xenophobia from other classical elements. After the birth of their daughter Ember, they set up their Blue Flame which represents their traditions and start their own convenience store called the Fireplace. Several years later, Bernie intends to retire and give Ember the store once she can control her fiery temper.
One day, when Bernie allows Ember to run the shop on her own, she becomes overwhelmed by the customers and rushes to the basement. Her fiery outburst breaks a water pipe, flooding the basement and summoning Wade Ripple, a water element and city inspector, who notes the faulty plumbing. Despite Ember's attempts to stop him, Wade travels to City Hall and reluctantly files a report of his findings with his air element employer, Gale Cumulus, who will have the Fireplace shut down.
Wade brings Ember to Cyclone Stadium to persuade Gale to reconsider the shutdown of her father's store. Wade mentions to Ember that he was investigating a leak in the city's canals before ending up at the Fireplace, and suggests to Gale that he and Ember can track the source of the leak from the store. Gale offers to forgive the violations as long as they find and seal the leak by the end of the week. While searching the canals, Ember and Wade discover a hole in a dam that allows wave runoff from ships to flood the city's plumbing, so they close the hole with sandbags.
The two spend time together in the city and learn more about each other. The sandbags eventually fail, so Ember melts the sand into glass to form a sturdier seal. Ember visits Wade's family at a luxury apartment, where she uses her fire to fix a broken glass pitcher, impressing Wade's mother Brook, who recommends her for a glassmaking internship. While playing "the Crying Game", Wade makes Ember cry by admitting he has feelings for her. Gale calls Wade and approves Ember's glass seal, thus saving the Fireplace from closure. Ember then realizes that she does not want to take over the store.