The Uninvited Guest(El habitante incierto)

What if ... you let a stranger into your house to use your phone, but while you've been patiently waiting in the kitchen, he just disappears ... or does he? Félix, an architect who has just split up with his girl-friend and inhabits a huge mansion in Barcelona, finds out how many hiding places there really are in his house. But are there enough to hide another person, a strange parasite of living space? Or is Félix really going insane?