Shenxiu (voice of Tingwen Wang) was abandoned by her mother (voice of Jing Ji) when she was a child. Since then, she has bad dreams about a monster called "Nightmare". One day, she travels on a cruise ship with her family. On a stormy night, she sees "Nightmare" on the deck, humming her mother's song and calling her to the sea. She falls and breaks into the fancy "Deep Sea" restaurant, an old transformed submarine. She meets the Chef, Nanhe (voice of Su Xin), and embarks on a mysterious journey.