The Black Emporium is received in Act 1 if the Black Emporium is available.
You do not know who I am, but I have heard of you. I understand you might need items from my collection, as well as the means to obtain them. I do not extend this invitation to anyone—but you are not simply anyone, are you?
Consider this an invitation to the Black Emporium. Instructions through the passages underneath the city are included with this letter, as is the charm to enter. If you give the charm to another, its permission will immediately be revoked... and the consequences unpleasant.