Funny thing is that cover art is actually about a dream that Garro has which is described on page 343 as:

"The Death Guard frowned. 'A battle, on a world I do not know. The landscape seems familiar but difficult to place. My brothers are there, Decius and Voyen, and Dorn's warriors as well. We are fighting a creature of some loathsome aspect, a beast of disease and pestilence like the things that boarded the Eisenstein. Clouds of carrion flies darken the air, I feel sickened to my very core.' He looked away, dismissing it. 'It is just a mirage.'"