In M32, during the War of the Beast, Lhaerial was dispatched by Eldrad Ulthran on a near suicidal mission to infiltrate the Imperial Palace and deliver a message to the Emperor himself. Ultimately, Lhaerial was captured and all of her companions were killed by the Adeptus Custodes at the foot of the Eternity Gate. Though Captain-General Beyreuth wished the Shadowseer executed, Lhaerial was saved by the intervention of Grand Master of Assassins Drakan Vangorich and Inquisitorial Representative Veritus who wished to interrogate her. During the interrogation, Lhaerial insisted her mission had been one of peace and as an olive branch she revealed the tooth of a Nocturne Drake supposedly given by Vulkan to Eldrad. Lhaerial went on to reiterate that Ulthwe had calmed the Warp in Segmentum Solar to aid the war effort against the Orks, but that their threat would pass and the Primordial Annihilator remained the true peril for the galaxy.
Following the death of The Beast at the hands of the Imperium's forces, Inquisitor Wienand secretly freed Lhaerial and gave her an Inquisition vessel to escape the Sol System. In doing so, the Inquisitor hoped that the Shadowseer would become an ally of the Imperium, who could be depended on to aid them in the future.