Toiling silently amongst the residents of an everyday Barcelona apartment building, doorman Cesar (Luis Tosar) harbors a dark secret: his sole desire in life is to make others unhappy. When he sets his sights on Clara (Marta Etura), one of his building’s cheeriest residents, his sick need blossoms into a full-fledged obsession. Embarking on a series of private and physical violations against Clara, Cesar becomes determined to ruin her life by any means necessary. Becoming the boogeyman hiding under the bed and bringing her nightmares to life, his fascination with torment soon crosses the line into lunacy - and his thirst for others’ sadness soon becomes manically unquenchable.