Apartment concierge Cesar (Luis Tosar) is a miserable person who believes he was born without the ability to be happy. As a result, he decides his mission is to make life hell for everyone around him. A majority of the tenants are easy to agitate, but Clara (Marta Etura) proves to be harder than the most. So Cesar goes to creepy extremes to make this young woman mentally break down. Things get even more complicated in this twisted relationship when her boyfriend, Marcos (Alberto San Juan), shows up.