Ultramarines 4th Company - Defence of Tarsis Ultra: With warning of the approaching Tyranid hive fleet given, the Imperial response was unusually swift. The Ultramarines contacted a brother Chapter of Space Marines, the Mortifactors, though they had diverged considerably from the ideals of Roboute Guilliman -- embracing a culture of death worship. A fleet led by the Imperial Navy Admiral Bregant de Corte aboard the battleship Argus was assembled, including many ancient and noble ships of war; the Sword of Retribution, and the Kharloss Vincennes to name but two.Imperial Guard soldiers from the Death Korps of Krieg and the Logres Regiments were shipped in and the local Planetary Defence Forces trained by Sergeant Learchus using the methods of the Ultramarine training barracks. Inquisitor Lord Kryptman once again lent his expertise to the commanders of the defence of Tarsis Ultra as well as bringing an elite Deathwatch Space Marines Kill-team led by the justly famed Watch Captain Bannon. As far as any world could be defended, Tarsis Ultra was as secure as it could be made given the time available to its defenders.Battle was joined in the system's outer reaches and though the world of Barbarus Prime was lost to the Tyranids, the first elements of their fleet were defeated. The advance of the Hive Fleet could not be stopped and Kryptman was forced to sacrifice the world of Chordelis -- ordering the Mortifactors to Virus Bomb it from orbit before the Tyranids could assimilate its biomass. Despite fractures appearing among the Imperial commanders, the Tyranid threat was met with courage and honour on the surface of Tarsis Ultra, though the defenders were hard-pressed to stave off the relentless attacks of the aliens.Though many thousands of lives were lost, and a huge proportion of the 4th Company was slain, the Tyranids were once more defeated when Captain Ventris cast off the teachings of the Codex Astartes and took command of the Deathwatch Kill-team. He led them on a last, desperate mission to deliver a lethal gene-poison to the heart of the last remaining Hive Ship.Having once served with the Deathwatch, Captain Ventris knew that this was where he could do the most good, and despite the grim warning from Veteran Sergeant Learchus that Marneus Calgar would hear of his flouting of the Codex, he set off on his mission. Through alien terrors and biological horror, the Deathwatch Space Marines and Captain Ventris were successful and the gene-poison was administered to the Tyranid Norn-Queen.Driven into spasms of uncontrolled mutation, the Norn-Queen died and her death throes drove the slave Tyranid organisms connected to her via the gestalt psychic consciousness of the Tyranid Hive Mind into paroxysms of feral self-destruction. The Tyranids were defeated, but like Ichar IV before it, the genetic taint of the alien invasion would forever be impossible to remove from the surface of Tarsis Ultra -- and the souls of its surviving population.With Tarsis Ultra secured, the 4th Company gathered its dead and returned to Macragge, the hearts of its warriors heavy as they contemplated the cost of honouring their ancient debt. But something worse was awaiting the 4th Company upon their return to their homeworld. Allegations of heresy awaited Uriel Ventris for his actions on Tarsis Ultra and with them, the potential to strip the company of its honour.