Elisa (Sally Hawkins) is a mute, isolated woman who works as a cleaning lady in a hidden, high-security government laboratory in 1962 Baltimore. Her life changes forever when she discovers the lab’s classified secret – a mysterious, scaled creature from South America that lives in a water tank. As Elisa develops a unique bond with her new friend, she soon learns that its fate and very survival lies in the hands of a hostile government agent (Michael Shannon) and a marine biologist (Michael Stuhlbarg).