It is 1962, and Elisa Esposito-mute her whole life, orphaned as a child-is struggling with her humdrum existence as a janitor working the graveyard shift at Baltimore's Occam Aerospace Research Center. Were it not for Zelda, a protective coworker, and Giles, her loving neighbor, she doesn't know how she'd make it through the day. Then, one fateful night, she sees something she was never meant to see, the Center's most sensitive asset ever: an amphibious man, captured in the Amazon, to be studied for Cold War advancements.

The creature is terrifying but also magnificent, capable of language and of understanding emotions... and Elisa can't keep away. Using sign language, the two learn to communicate. Soon, affection turns into love, and the creature becomes Elisa's sole reason to live. But outside forces are pressing in. Richard Strickland, the obsessed soldier who tracked the asset through the Amazon, wants nothing more than to dissect it before the Russians get a chance to steal it. Elisa has no choice but to risk everything to save her beloved. With the help of Zelda and Giles, Elisa hatches a plan to break out the creature. But Strickland is on to them. And the Russians are, indeed, coming.