There is an ancient pond at Caerlin Howe Farm. On finding her drowned husband there, pensioner Abigail vows to destroy the menacing water and its mockingly heart-shaped plants. Damp suddenly appears about her home. She has strange nightmares and begins sleepwalking. Realizing she has stirred up far more than the mud, the grandmother begins to fear for her sanity and the very lives of her remaining loved-ones.