We open up with a doctor discussing his new patient with Pescara: it's Ferdinand, who has apparently be laid low by lycantrophia.
Lycan-what-now? This is more or less what it sounds like: Ferdinand has been struck by a mysterious disease that's made him go crazy and have episodes where he thinks he's a wolf. Yes. A wolf.
For the moment, Ferdinand's less-rather-than-more crazy, but apparently he's been running around graveyards at night, digging up bodies and howling. Yeah. Full-on nutjob.
Ferdinand comes in, accompanied by Malateste, Bosola and the Cardinal.
He starts acting like a lunatic, speaking nonsense and trying to strangle his own shadow.
The Cardinal lies, and explains that Ferdinand's sudden onset of crazy is due to him having seen the ghost of a murdered woman.
Bosola asks to speak the Cardinal alone, and the Cardinal secretly says that he has to keep Bosola from figuring out that he also had a part in arranging the Duchess's death: he figures that Bosola only knows about Ferdinand's involvement.
He pretends to not even know that the Duchess is dead, and commissions Bosola to seek out Antonio and have him killed.
Meanwhile, Julia comes in and, as she walks out, remarks that, hey, that Bosola is kind of a hottie.
Bosola agrees to find Antonio, but as the Cardinal leaves, he remarks to the audience that he knows the Cardinal's lying about not knowing the Duchess is dead. If the Cardinal's going to lie to him, he's going to lie to the Cardinal: he has no intention of killing Antonio.
Apropos of nothing, Julia comes in, pointing a gun at Bosola. Just go with it.
This is, apparently, her way of wooing Bosola. We're sure the Courting-At-Gunpoint trick works all the time for her.
Bosola, reasonably, doesn't believe her, but even after his attempts to rebuff her she insists, "no, Bosola, I'm really into you. Having met you like three minutes ago."
Bosola takes stock of the situation and figures, "hey, this is the Cardinal's mistress, I can totally use this to my advantage."
"If you really love me," he says, "you'd do me a wee little favor. The Cardinal's got something on his mind, and I want to know what it is."
She agrees to find out what's bothering the Cardinal and report back to Bosola the following day.
Bosola leaves Julia, and in comes the Cardinal.
Julia's not as dear to the Cardinal as she thinks she is—when he sees her, the Cardinal complains to himself that she's his "lingering consumption"—apparently he's getting tired of his mistress, and is looking for a way to get rid of her.
Julia then proceeds to ask him what's been bothering him. Even though the Cardinal repeatedly tells her she can't handle the truth, Julia continues to badger him and promise that she won't tell anybody until he gives in.
"Fine. Wanna know what's been on my mind? I just had my sister and her kids strangled a few nights ago."
Julia's taken aback, and replies that the Cardinal was right, she can't keep that secret.
The Cardinal has her swear upon a book to keep quiet, and has her kiss the book to seal the deal.
Bad move, Julia: apparently, the book was poisoned, and now Julia has moments to live.
Bosola bursts in, things clearly not having unfolded the way he'd planned, as Julia croaks.
In the subsequent exchange, Bosola professes that he still intends to kill Antonio, even though it's clear that he knows the Cardinal had a hand in the Duchess's murder.
The Cardinal gives Bosola the master-key for their palace, so that he can surprise Antonio and kill him.
Once the Cardinal leaves, Bosola confesses that he in fact means to save Antonio, and take him as far away from the brothers as he can.