Gydrael was selected for a tour of service with the Deathwatch for several reasons, including his prowess when it came to perceiving, compartmentalising and recalling information. In addition, Gydrael's olfactory receptors were enhanced by surgeons of the Ordo Xenos, enabling him to pick out spore-trails and recognise a wide catalogue of alien scents (with the caveat that Gydrael was unable to deactivate this).
Shortly before he left to undertake his tour of service, Gydrael secretly met with Interrogator-Chaplain Asmodai. Asmodai confided with Gydrael that the Deathwatch was just one of many ways the Unforgiven used to seek out and eliminate The Fallen, which Gydrael acknowledged.
On one mission for the Deathwatch, Gydrael was part of a Kill-Team led by Sergeant Decurius. They were tasked by the Ordo Xenos with wiping out a Sslyth infestation on the planet Kolagar, which the Inquisition had identified as a potential threat to the progress of the Vensine Crusade. The Kill-Team was ordered to infiltrate the aliens' nest, constructed within a mountain called Phoenicus Peak, and detonate a set of three Virus bombs gene-crafted to the phylum of Sslyth on Kolagar.
Both Gydrael and the Inquisition also suspected that the appearance of the Sslyth on Kolagar was not a coincidence, and it was eventually confirmed that the Ssylth were actively working with the Chaos Space Marines of the Emperor's Children Traitor Legion, who were responsible for the uprisings and rebellions plaguing the Vensine Sector in the first place.
Gydrael, along with his kill-teammates Thorne and Hasdrubal, proceeded to infiltrate the xenos breeding grounds, fighting off Sslyth guards. However, Gydrael also encountered some of the Ssylths' allies - the Fallen Angel Averamus and the Emperor's Children Dreadnought Ancient Xezukoth. Gydrael was able to kill Xezukoth by noticing a partition in the Dreadnought's armour that functioned as a mouth and impaling Xezukoth through the mouth with his power sword as the Dreadnought prepared to eat him. Unfortunately, during Gydrael's encounter, his kill-teammates had no choice but to detonate only two of the three virus bombs, resulting in no cascade reaction taking place. Averamus had also managed to slip away. The remaining Sslyth-cleansing on Kolagar was left to the Astra Militarum, with predictions that many men would die in the process.
- 1: White Dwarf 109 (2016) — Kill Team Cassius
- 2: Deathwatch: The Flesh of the Angel (Short Story) by Ben Counter