Dark Pattern - Derleth Lexicon: The matter of the Derleth Lexicon first came to light a decade ago in the early ninth century of the 41st Millennium, when the Omega Vault at the heart of Watch Fortress Erioch unsealed itself in a most extraordinary manner.Many openings of the vault are in some way predictable, with Librarians and other psykers present in the watch fortress at the time receiving some form of premonition or at least an inkling that some portentous event is about to occur. In the case of this particular opening, no such warnings were received.Indeed, the local region of the Warp was noted as especially still, though, later on, this fact would be used to retrospectively identify that something was indeed amiss.It was in the depths of watch secondus and the majority of the fortress was silent and still. Whether by coincidence or unseen design, an unusual number of Kill-teams were absent, having been deployed on a range of pressing missions the length and breadth of the Jericho Reach.Watch Captain Brand Mac Lir, a formidable and experienced Veteran from the Storm Wardens Chapter, had the watch when, with no warning at all, the fortress' defence grid came to maximum alert and warned of an imminent assault by an as yet unidentified foe.Brand instigated a full response, and those Battle-Brothers present on the fortress mustered for what the wailing klaxons promised to be an attack of unprecedented scale. As automated defence turrets swept the darkness for any sign of a target, the Kill-teams armed themselves and swore that, should they fall, the watch fortress would be denied to their enemy.So overwhelming was the scale of the alert that Brand was forced by long codified protocol to unseal the outer wards of the fortress' Plasma Reactor containment shields so that in the event of enemy victory the entire station might be destroyed, along with all of its terrible secrets.Then, just as suddenly as it began, the alert was ended. Furious, Watch Captain Brand ordered an immediate investigation into what had triggered it, unable and unwilling to accept that the Deathwatch's defence grid had been triggered in error.Of course, the alternative was just as terrible to consider, for if an enemy had been so near to breaching the Deathwatch's defences, it had come closer than any ever had and survived.In addition to ordering his Techmarines to conduct a full audit of the fortress' defence augurs, Brand set every available Battle-Brother and Chapter Serf to a complete search of the Deathwatch's space-borne citadel. No corner was left in shadow, and chambers and passageways not unsealed in long centuries knew the unfamiliar tread of the station's inhabitants.The possibility that something, no matter how seemingly insignificant, might have slipped through the Deathwatch's defences was simply too dreadful to contemplate, and with so many souls scouring the watch fortress it was not long before something was indeed discovered.The portal to the Omega Vault was found open, an eerie, actinic glow emanating from its silent depths. It was Watch Captain Brand himself that passed into the vault to recover the latest of its mysteries, for surely the activation of the fortress's defences at the moment of its opening could be no coincidence.That mystery proved to be a simple book bound in withered leather, a tome that would in time become known as the Derleth Lexicon after the individual identified as its compiler.