Descent
The book cover is what I imaged it looks like.
Red spider lilies symbolize death. They are associated with final goodbyes, and legend has it that these flowers grow wherever people part ways for good. In old Buddhist writings, the red spider lily is said to guide the dead through samsara, the cycle of rebirth. In Japanese, "Manjushage" for red spider lily means "flower of the heavens.
Remember when William mentioned that Proserpina's veins glows red in Chapter Ten? It was because of the tattoo as well–her marking literally burns her skin and nerves which is actually the same curse Hades gave her in the Prologue.