In order to find the truth, she fell into the abyss of darkness. Whether it is skills, beauty or personality, Yi Ling (played by Shin Min Ah), known as the "diving queen", seems to have everything. However, her only regret is that she can't swim with her friend Xiuzhen (played by Lee Yoo-young). In order to help Xiuzhen, Yi Ling changed her main activity to water ballet. While the two friends put all their efforts into it, they disappeared without a trace because of an accident. Although Yi Ling survived, she also lost her memory. When Yi Ling slowly regained her memory, another side of Xiuzhen that she didn't know at all emerged in her mind, which also shook her belief in the road of diving...