A law school professor witnesses his colleague, friend and mentor murder his own wife. Rather than turn his friend in, he disowns him, but the decision leads to more danger.
Young psychologist Martín Mondragón is contacted by a mysterious man named José Sagasti, who tries to collect an old debt that Martin's grandfather left when he died. Rivera, being the first male descendant, is the most suited guarantor to pay off the debt, which consists in giving his soul to the devil by dropping a bit of blood from an old parchment.