The Coven of Isha is a secret pact between some members of the Ordo Xenos and the ancient Farseer Eldrad Ulthran of Craftworld Ulthwé. According to the Coven's librarium, the information provided by the Eldar through this pact has been linked to a number of disastrous events that engulfed the Imperium of Man, including the Sanapan Scouring, the Mortis Annihilation, the Third Coming of Orian and the First War for Armageddon. The Coven has rarely been invoked, for the Eldar rarely require the help of the Imperium, and the Imperium never looks toward xenos for help. The most recent time that the Coven was activated was when Deathwatch Space Marines from the Ordo Xenos had to help the Craftworld Ulthwé to counter the Dark Eldar's recent raids that took many Ulthwé prisoner to Hesperax, the homeworld of Lelith the Wych Queen. The prisoners were taken to be slain in Hesperax's gladiatrix games.
The great Eldar Farseer Eldrad Ulthran had created a special Wraithbone chamber hidden aboard the Inquisition's secret space station located in the Ramugan Sub-sector for the Ordo Xenos which could be used for communication between the Inquistion and the Seer Council of Ulthwé. The Inquisitor Lord Seishon was summoned there to hear the request of Ulthran that the Imperium aid the Eldar in securing Craftworld Ulthwe by recovering a lost Eldar relic. The Inquisition's Ramugan space station had stood for millennia, and dated back to the time of the Great Crusade when the Emperor Himself was still actively leading the Imperium. The station was home to delegations from the three main branches of the Inquisition: the Ordo Xenos, the Ordo Hereticus and the Ordo Maulleus.
The Seer Council of Ulthwe was convinced to accept aid from the "Mon-keigh", an action that some members of the Council, such as Ruhklo, saw as an insult, but the Emerald Seer Thae'azki and the Seer Eldressyn, who had been chosen to serve on the Council by Ulthran himself, insisted on accepting the humans' aid. At last the decision was made. A Deathwatch Kill-team departed from Ramugan on the Lance of Darkness frigate by order of the Ordo Xenos to recover the relic for the Eldar and uphold the Coven of Isha. The Kill-team included the excellent Astartes from some chapters, Emperor's Champion captain Octavius originally come from Imperial Fists, chaplain Luthar from Revilers Vigilant, librarian Ashok from Angels Sanguine, Kruidan of Mantis Warriors, the Iron Father Sulphus from Red Talons and Pelias, Sergeant of the Black Consuls. They soon join a conflict against a Dark Eldar's raid. Realising the Guardian of Ulthwe were such wimps, and the darkned soul of Ulthwe's citizen, they barely had a gut to stand a ground and will retreat when aid come, even from the "mon-keigh". Next, they followed the request to patrol the Khalandhriel’s Hall of Ulthwe from warlock Shariele, and confronted some Dark Eldars troops there. Abruptly, Ashok dissapered, it later to show up that he was ordered by Lord Inquisitor Seishon to find the Infinity Circuit of Ulthwe and set up a beacon there so that the Inquisition can keep track of Ulthwe should it depart, and he successed. However, he was captured, disabled and taken to Hesperax by the Ulthwe's seers as a "gift", a secret bargain between the Emerald Seer Thae'azki and Lelith.
After wrecking havoc on the raid, the Deathwatch Kill-team was summoned to the seer council and was allowed to patrol the space and find traces of Dark Eldar movements. The Lance of Darkness depart, bring the whole team and two accompanied Eldar, warlock Shariele and Shining Spears's Exarch Dhrykna. They soon find a squadron of Dark Eldar Corsairs, and gave a chase. The Corsairs were no match for the Lance of Darkness, and only one of them escaped the assault, by order of Captain Octavius so that they can find the Dark Eldars's base.
- Warrior Coven (Novel) by C.S. Goto, pg. 12