In 1950s Spain, Montse (Macarena Gómez) cares for her younger sister, played by Nadia de Santiago. Montse works from her home as a dressmaker and is an agoraphobic, wholly dependent upon her younger sister for assistance. At the opening of Musarañas, her younger sister has just turned eighteen and is showing strong signs of independence: she works outside the home; and Montse has noticed, from her window, her younger sister conversing with a young man in the street. The sisters’ mother died during the birth of the youngest and the two were raised by their strict, religious father. He has since disappeared, leaving the rearing of Montse’s younger sister upon herself. Her father’s religious conviction is strong within Montse, and when her younger sister arrives late one evening, Montse takes to corporal punishment upon her. In the morning, Montse begs for her sister’s forgiveness, but it seems their tenure together is destined to end. The handsome upstairs neighbor, Carlos (Hugo Silva), injures himself falling down the stairs and he knocks at Montse’s door seeking help. She puts Carlos in the spare room, and tends weakly to his wounds. She promises his recovery, yet Montse begins drugging him. Her younger sister wants to escape and is determined to help Carlos leave, as well.
Musarañas is Montse’s film. She is the protagonist and the antagonist of the film. Almost the entire film takes place in Montse’s flat and when the film ventures outside, it is only into the landing outside or Carlos’s flat upstairs. Andrés and Roel expend quite a bit of time fleshing out her character and making her sympathetic to the audience. It is revealed that her father was extremely abusive towards her and she had to endure this for quite some time. Understandably, she is agoraphobic and fearful as her father kept a tight grip upon her. When Carlos comes into her home, one can see why she is keeping him close. In a romantic sense, this is really only Montse’s opportunity to fall in love. Of course, Montse is also completely unhinged; so when Musarañas needs her to become a monster, she becomes one. In a move, like a schism, all of the sudden Nadia de Santiago’s character (whose name is never uttered by the way) will become the protagonist: she attempts to protect Carlos from Montse, and it is the younger sister with whom Carlos falls in love. When Carlos’s disappearance attracts the police and his fiancé, Elisa (Bang), Montse begins a murder spree. With each subsequent corpse that she has to hide in her flat, Montse becomes desperate and ruthless. In the gory final act, Montse does not appear as a person at all. Conveniently, Musarañas attempts a reconciliation between the sisters in the final minutes, and a revelation occurs between them that was painfully obvious to the viewer from the opening minutes.
Macarena Gómez, as Montse, gives a stellar performance. She is the sole reason for seeing Musarañas. No other character is treated with any sensitivity. Musarañas begins as a fascinating character study but quickly and conveniently decides by its third act to become a bloody horror movie. Adept filmmakers could have blended the two, but Andrés and Roel were not up to the task. A pity.