"with several incoherent threats of retaliation that, in their infinite depth of virulency, smacked of King Lear"

In this reference to Shakespeare's tragedy King Lear, Lockwood is comparing his own rather empty, maniacal threats with those of the rambling, bitter Lear. In Act 2, scene iv, Lear utters these disjointed, spontaneous lines born of a dreadful anger:

I will have such revenges on you both

That all the world shall - I will do such things -

What they are yet, I know not; but they shall be

The terrors of the earth!

It is probably coincidence, but Lockwood's two Shakespeare references, just pages apart, both come from the fourth scene of the second act - Da Vinci Code fans may conjure up a theory...