The Tyranids 017M42

The Tyranids have ravaged the Aleph Sector on a number of occasions. Hive fleet Leviathan spawned several splinter fleets, namely Megalodon, Morph and Triton, which ravaged the southern reaches of the sector, destroying Orvicare and leaving several worlds uninhabitable. But far worse was Nemesis, of unknown orogeny and entering the sector from apparently within Imperial Space, this ultra intelligent Hive fleet laid waste to much of the Zadoc subsector before disappearing into interstellar space. Just before the Great Rift appeared, Nemesis had resurfaced in the Perseus Deeps.

Now the Hive Fleet is loose, somewhere, in the vast depths of space in the Dark Imperium. The motivation to feed is strong but Nemesis in particular has been known to employ particularly elaborate strategic moves, rather than to just devour whatever it comes across. Nemesis will withdraw if outmatched, and has proved a deadly foe in the sector. One the Imperium at least must now deal with without reinforcement.