It's Thursday, and already some people are getting a chance to see the new Deathwatch Overkill box. I read through part of the backstory in the box set, and of course some of the spoilers, but I will let you decide if you want to read those. The backstory for the Genestealer Cult is expanded upon in these.
Lady Atia left this link for us in the comment sections
So head over and check them out. Only the last one contains the spoiler for the end of the story. So just don't check that one out if you don't want to know
You can also see a complete set of leaked images over on Bols