"Secure their weapons." The mortal commanded, gesturing to his subordinates.

The three Grey Knights balked, dropping into combat stances. Artorias spoke, "No one disarms the Grey Knights of the Holy Emperor."

The mortal drew himself to his full height, diminutive in comparison to the Space Marines, but his sheer force of will shone like a beacon to their Warpsight. "By order of Malcador the Sigillite, primogenitor of your order, by order of the Emperor of Mankind, and by order of the O5 Council, I demand the surrender of your weapons. There are... Things far more dangerous than Chaos in our vaults. Our remit is unmatched, our authority absolute." He held up a signet ring, and placed it firmly in the lead Knight's gauntleted fist.

The Knight looked at the ring and immediately surrendered his Null Stave. The others paused significantly but followed suit.

The Mortal nodded, "You would not be here if it wasn't absolutely necessary. We require your expertise." He turned and strode briskly through the enormous baroque doors, which opened for him silent and smooth.

They followed.

An interminable march of twists and turns past doors labeled with alphanumeric signifiers later, they came to a door. A brutal slab of adamantium and titanium alloys, with a variety of esoteric warnings on the wall nearby.

KETER HOSTILE LIFEFORM

The Knights shared a look as the Mortal spoke again, "When you enter this room, you will encounter an organism. It is nonhostile to Psykers. Please attempt to ascertain it's True Name and banish it."

The door slid open, revealing another massive door. The Mortal gestured and they entered. As the door swung shut behind them, Damocles voiced the thought they shared, "They sent us to a Daemon, unarmed."

Silence greeted him as the second door opened.

Within the next chamber was a large transparent container of boiling acid, the fumes filling the room were lethal, and the armor threat sensors of the Knights went berserk.

Inside the vat a distinctly inhuman skull bumped the glass, eyes rapidly forming and dissolving. A raspy, gurgling voice emanated from the tank, "Humans."

Artorias stepped forward, "We are His Holy Grey Knights, the Blade of the Emperor, Chamber-Militant of the Ordo Hereticus."

"You've come to kill me." It wasn't a question.

Regulus cut in, "We've come to send you home."

The creature considered, floating in it's deadly bath. "If you're being truthful, I welcome you. Let me out."

Artorias silently disengaged the systems filling the vat, from a nearby control panel. The acid drained, leaving a pitiful but large corpse. It's legs planted themselves as it leveraged itself up, tendons and muscle and flesh rapidly racing across bones to recreate it's body.

The beast regarding them was reptilian, huge, powerfully muscled, and clearly intelligent. It paced around them, menace exuding from it like an odor.

Finally it stopped and sat, somewhat like a dog. "How do I go home?" It intoned coarsely.

Artorias nodded, "Tell me your name. Your True Name."

The beast spat a disgusting sounding litany of guttural, unpronouceable noises. "Good luck repeating it."

Artorias nodded at Damocles, who concentrated his psychic might and started reciting the name, each sound an exact copy of the Creature's.

As he finished, the Beast stood, almost alarmed. Damocles spoke, "I command you to return from whence you came, in the name of the Emperor."

It started to rush forward as an unseen force gripped it with strength beyond reckoning. "WAIT! I CAN'T GO BACK! I DON'T KNOW THAT WORLD ANYMORE!"

Damocles looked at Artorias, at the beast that was desperately clawing to remain in the Material realm. Then he intoned with fervor, "You are banished!"

In the observation chamber, the O5 Council watched in amazement as SCP-682 finally died, at least in their estimation. An ancient file was retrieved, opened, and stamped with two new classifications, "Neutralized" and "Safe".

Deep in the bowels of the Warp, the Beast was home.