Dumbfounded, and deeply concerned for the man seems to be intent on...on...what, Will is not sure.
But he knows one thing. He has no understanding whatsoever of that which the man rants and raves.
Calmly he waits until the man, this Iago, is done. There is much that wants explaining, but his once-host, now-berator is of no mind nor attitude to be of any help. The names Othello, Desdemona, and especially Iago mean nothing to him. And what is this accusation's meaning? He is not a god. He has no control over any living being; that is a role he's never wished to play.
At last Iago finishes. Will waits a choice moment, certainly not frightened of the man for he himself is strong though still weary, and at last speaks.
"You know me, Iago, but I know not you. You speak of things I do not understand, and I suspect you well know it. Who is this Othello, this Desdemona.... You? The man I see before me is made of flesh and blood, and presumably thus capable of his own decisions, responsible for his own doings. You are not a fiction, a character in a play to be, as you say, a puppet. I know not of what you speak.
"Yet you seem to blame the blameless for something presumably in my control. I assure you, I know not you, nor they who you mention. I am a playwright, simple put. I write fiction. Fiction! Stories! Tales for the masses! ENTERTAINMENT!.
"I am not of this time. I came by accident, having been assisted by a remarkable man and my Queen's enemy, the Doctor. And, of course, his lovely Dark Lady, Martha. He opened my eyes to possibilities even I in my supposed god-like state would never have fathomed. He opened my eyes to the possiblity of time. But what you speak of is impossible--why man, you speak as if you believe I wrote you! Impossible!
"You speak to me as if I am your enemy, that you bear me hatred. We have not met, man. Have not met! And if you are a time traveler, as the Doctor and his Lady were, then perhaps it is possible we will meet in a time and place I do not yet know. And yet, even so knowing that is a possibility--you act as I, William Shakespeare, are a villain, a beast, for making you do things to which you vehemently object.
"I am not that sort of man to force unwanted will on another, I assure you. I am not a cruel man, though there are none here who can vouch for me.
"So you must forgive me. You believe I have wronged you, and I believe it is impossible, at least not as I am, sitting here, facing you."