The story takes place in 1963, during the Cold War, when the mute girl Elisa (Sally Hawkins) worked in a government laboratory as a cleaning lady. When she was young, a serious illness took away Elisa's voice. Since then, she has lived a lonely life in silence. All her friends are the painter old man (Richard Jenkins) and colleague Zelda (Octavia Spencer). One day, the laboratory sounded a high alert alarm, and a mysterious jar full of water was sent in. Elisa was shocked to find that there was a strange creature that was half man and half fish in the jar. Under the leadership of Richard (Michael Shannon), the team of scientists wanted to extract substances that could make biological weapons from this monster, but in Elisa's eyes, it was just a lonely life form like herself. As time went on, Elsa and the monster actually developed feelings.