Kill and Be Killed(1962)

Original title: A hierro muere

A former singer lives alone with her fortune - and with her nephew, Fernando, a low character to whom she refuses to lend more money. Elisa leaves prison and starts a new life as a personal attendant to the aging singer, using her knowledge as a former nurse - a profession she can not return to. Fernando meets Elisa, and together they plan to poison the lonely woman, and use her money abroad. They plan their alibis well. But those who kill by the sword will perish by the sword.