The blood-drenched Traitor Marine stood proudly before Lucatar, the skulls impaled upon the spikes crowning his trophy rack watching the scene play out through shadowed eye-sockets. They stood alone upon a desolate stretch of moorland, facing one another like combatants in a gladiatorial arena. At Lucatar's back a settlement burned, the screams of dying humans filling his ears. A woman lay at the traitor's feet, the front of her simple homespun dress wet with blood; her tear-streaked face was turned towards Lucatar, her soft brown eyes wide and imploring. The traitor kept the curved edge of his power-scimitar poised above her slender neck, yet his helm's malevolent emerald eye-lenzes remained fixed on Lucatar.

"You are so young," the traitor said, his voice emerging harsh and contemptuous through his vox-grille, "little more than a boy. Are the masters of your Chapter in the habit of sending out mere children to fight in the place of true warriors?"

Lucatar gripped his battered chainsword in both gauntlets; he did not know what had happened to his bolter. His mind raced as he considered how he might save the woman, or at least provide her with an opportunity to escape. "Come and cross blades with me, oathbreaker," he challenged, raising his weapon before him like a duelist, "then we'll see how much of a warrior I truly am."

"I could take your head in half a heartbeat, whelp," the Traitor Marine sneered, "I could kill you just as easily as this sniveling bitch here," he dug a boot roughly into the woman's side and she cried out in pain as several ribs fractured. "So fragile," the traitor snorted in disgust, "so weak, so pathetic – and to think the False Emperor created us to serve such wretched creatures…"

Lucatar felt his blood boil at the fallen Astartes' callous disregard for human life, yet kept his emotions in check – if the traitor realized he desired to rescue the mortal he would swiftly slay her out of spite; he had to act as if her presence meant nothing to him, that she was beyond his consideration.

"You will not find me fragile or weak, heretic scum," he said, baring his teeth and advancing a step, "I will put you down like the mad dog you are; I will lay your helm at my captain's feet after my brothers have driven your warband from this world – this I swear by the bloody tears of Sanguinius."

The traitor laughed scornfully. "Ah, yet you are weak, Lamenter!" Snatching the woman up from the ground he flung her at Lucatar in one fluid motion; he reacted instinctively without conscious thought, and the teeth of his chainsword tore her oncoming body in two, showering his warplate with gore. Then the traitor was upon him, his scimitar a blur of energized steel as it stabbed and cut. "Your Chapter's reputation precedes you, for what other Astartes brotherhood would still cleve to their 'duty' despite being scorned and shunned by an Imperium that hates them? Only deluded fools who believe humanity's existence is something worth preserving in a galaxy that knows only war and the eternal laughter of thirsting gods!"

Lucatar fell to his knees, his chestplate split open, his hearts pierced. Blood was in his mouth and his vision was tunneling. The traitor drew his bolt-pistol and leveled it at his forehead. "You have failed; die now and join your gene-father in hell."

"No!" Lucatar snarled, tears stinging his eyes, "Others will take my place! For those we cherish we die in glory!"

The Traitor Marine fired; a burst of searing light exploded through Lucatar's mind and he –

– convulsed in the restraint chair, pulling hard against the synthleather straps securing his limbs; a latticework of sensor-nodes covered his shaved scalp like a skullcap and he was surrounded by various monitoring devices that beeped continuously as they tracked his vitals and brain activity. Sweat sheened his naked body and his heart pounded wildly in his chest. Lucatar screamed as the aftershock of his simulated death tore through his psyche – the confrontation had been a theoretical test: a test he had failed. The woman had died; he had not even managed to slay his opponent. Perhaps, if he had been just a bit quicker…

"Send me back," he called out in desperation; he was alone in a hypno-indoctrination chamber, a cold, sterile room all the aspirants had come to dread, "Let me try again; I will save the woman and kill the traitor, I just need to be faster next time –"

The door abruptly opened and an Apothecary garbed in plain white robes entered, his broad transhuman face expressionless. "Please, lord," Lucatar begged as the Space Marine bustled around his chair, making minor adjustments to different machines, "I promise I'll do everything right if you –"

"This test is not about 'doing everything right,' aspirant Lucatar," said the Calix dispassionately as he shone a bright light into the boy's eyes, noting the dilated pupils, "It is not about saving the woman, nor is it about killing the traitor."

"Then what am I supposed to do?" asked Lucatar.

"There is a vital lesson you must be taught if you are to become one of us. It is one of the hardest, most important lessons of all."

"What? What is it?"

"That," said the Apothecary as he departed without a backward glance, "is what you are here to learn."

It took a long time for the lesson to sink in. He died countless deaths and looked on helplessly as countless other innocents died in turn. "What have you learned?" the Calix asked him after it was finally over. Lucatar raised his head and gazed up at the Sanguinary Priest with haunted, bloodshot eyes.

"I learned I won't be able to save everyone."

He paused, and took a deep, resolute breath.

"Yet I must never stop trying."