Yeok, a middle-aged teacher raising a son and a daughter alone, witnesses students fall to their deaths from the rooftop of the school where she works. Discovering that her daughter Hyejeong was also present at the scene, she presses her for answers, but Hyejeong only repeats the same words: 'There was a bird in the sky.' As the strange, unexplained deaths continue, Yeok, together with a reporter covering the case and a streamer who runs a birding channel, head towards the birds’ habitat.