Miranda has always been afraid of fireflies for as long as she can remember. Her fear stems from a story her older sister used to tell her when they were growing up. According to the story, fireflies were put on Earth as messengers for aliens on other planets. Supposedly, aliens inhabited Earth first and then left to explore what else the universe had to offer. They left a lesser species, fireflies, behind to communicate with them. Each time fireflies light up, it's in a unique code, not just a mating ritual. As Miranda grows up, she becomes a successful writer for a publishing company in New York. She meets a man by the name of Johnathan, who also works for the company. She learns that he is also familiar with the story her older sister used to tell her. Suddenly, the news is flooded with increasing UFO sightings all over the world. Additionally, plagues of fireflies are seen moving from rural areas to big cities. Miranda and Johnathan start to wonder if there may be some truth to the story. If so, does it mean the aliens are planning a return to Earth? What does that mean for the humans that now inhabit the planet?