Please answer the following question: What is the answer for the question: Who is Neil Broderick writing a book about? from the following article ?  A man unveils a valuable painting he picked up for $50,000 and is killed. A card with a large black ace (of spades) is put on his chest. Another "Black Ace" victim. The killer sends his victims a Black Ace card, warning them they are to die and then kills them, his way of taunting the police. Neil Broderick, an author, intends writing a book about him and is on his way to see Thornton Drake to get more information about him. Austin Winters is his secretary and Neil met his daughter Martha on the train, on the way to Chicago. Drake has just received a Black Ace, with the words: "At seven tomorrow night", the time he is to be killed. Two plainclothes cops arrive from police headquarters, having had a call, Clancy and Dugan (both incompetents). Martha suggests that they leave for Drake's Louisiana plantation tomorrow morning and be far away from there at seven tomorrow night. Drake agrees and suggests they all go. On the flight, the lights go off for some seconds and when they come on again, Austin Winters is dead without a mark on him. At the plantation, Clancy ineptly questions the suspects till Neil points out that they are now in another state, so out of their jurisdiction. Neil goes to another room and makes a phone call, then signals to someone outside. After he finishes his call, the line is cut. Meanwhile one of the pilots has taken off in the plane, leaving the other pilot, Henderson, behind who claims he does not know anything though he was out of the cockpit when Winters was killed. The coroner finds a letter on the dead man which is to be read if Winters dies. It will reveal the identity of the Black Ace. Clancy starts reading it aloud and unsurprisingly the lights go off and the letter has vanished when the lights are turned on again. People locked in their rooms that night and Neil has a hidden car outside signal to him.
A:
Black Ace