The Case of Mask Lady - S1.E552

A man walks into a prominent lawyer’s office late at night and asks him to handle his case. He claims that his life is in danger and would need the lawyer to take care of his masked acquaintance, in case he loses his life. He tears a small postcard and hands one half to the lawyer and the other to the masked lady. What secret does this poster hold? What is this mysterious man up to?