My group's encounter with Miss Book was...well, it felt a little cheap. Master Nonesuch was with her but we had Herrod and his team with us plus a few stormtroopers. The fight started with Herrod and our gigantic, combat psyker leaping into melee combat with her (since she was just laughing at our attempts at ranged attack on her) and they got their asses handed to them pretty much right off the bat (to put this in perspective this was the first time in many sessions I've ever seen our psyker not annihilate his melee opponent effortlessly. The man is a monster). I was busy hacking through her minions but once I was done I charged in to try and save our psyker who was unconscious at this point. What followed was basically me wailing on her for a while (I'm a double power sword assassin with over 40 strength, I normally pack a decent punch) but caused pretty much no visible damage before she started grappling me and left me on minus wounds. While this was happening Herrod's assassin, Darkly Hand, killed Nonesuch (who had been wrecking our ranged forces and killed half of Herrod's guys) and stole his one-shotting scepter of doom. He then jumped into combat with Book to help Herrod try and make her stop strangling me to death. He hit her with the scepter and killed her in one shot. So yeah, this one NPC killed both bosses. A little anti-climactic but then of course Herrod gave Darkly a nod and he swung the scepter at me, missed and I chopped him into hamburger before claiming his kills as my own. That's how it works, right?