Cryptogram from Frankenstein; or, the modern prometheus, chapter 24

But now, when I appeared almost within grasp of my foe, my hopes were suddenly extinguished, and I lost all trace of him more utterly than I had ever done before. A ground sea was heard; the thunder of its progress, as the waters rolled and swelled beneath me, became every moment more ominous and terrific. I pressed on, but in vain. The wind arose; the sea roared; and, as with the mighty shock of an earthquake, it split and cracked with a tremendous and overwhelming sound. The work was soon finished; in a few minutes a tumultuous sea rolled between me and my enemy, and I was left drifting on a scattered piece of ice that was continually lessening and thus preparing for me a hideous death.

The sentence you are solving goes here.

Oh! When will my guiding spirit, in conducting me to the dæmon, allow me the rest I so much desire; or must I die, and he yet live? If I do, swear to me, Walton, that he shall not escape, that you will seek him and satisfy my vengeance in his death. And do I dare to ask of you to undertake my pilgrimage, to endure the hardships that I have undergone? No; I am not so selfish. Yet, when I am dead, if he should appear, if the ministers of vengeance should conduct him to you, swear that he shall not live - swear that he shall not triumph over my accumulated woes and survive to add to the list of his dark crimes. He is eloquent and persuasive, and once his words had even power over my heart; but trust him not. His soul is as hellish as his form, full of treachery and fiend-like malice. Hear him not; call on the names of William, Justine, Clerval, Elizabeth, my father, and of the wretched Victor, and thrust your sword into his heart. I will hover near and direct the steel aright.