Tarkus burst into the clearing in a shower of leaves and broken branches. What he found was chaos. Samus knelt on the ground, screaming and laughing in equal measures. John was off to once side, covered in what appeared to be a dark purple blood, the obliterated corpse of some unfortunate creature plastered over everything around him. Tarkus made to approach them when a claw the size of his chest slammed down in front of him. He stopped short, looking up at the source of the attack. Suspended in the lower branches was an obese blob of light that glowed and pulsed with a sickly light. A number of tendrils dangled from its lower surface clustered above Samus and Tarkus and siphoning small wisps off of them from time to time. Tarkus felt his choler grow at the sight of the beast.
"Unclean thing of the Warp!" he bellowed, "I will see thee destroyed before I leave this place!"
The creature let loose a grating screech that made Tarkus's vision swim with its volume. It lashed out with another clawed tendril, which Tarkus side stepped swiftly. He drew his chainsword, revving into life, and hacked the limb in two. The daemon screeched again, this time in agony. Tarkus raised the boltgun in his other hand, loosing a salvo of bolts into the things body. The bolts detonated inside its gelatinous form, blasting oozing craters in it. The daemon shimmered, briefly going insubstantial before restoring its stability. Tarkus used the creature's dissolution to close on Samus, who was closest to him. Taking the chainsword in a two handed grip, he swung high and severed the tendrils holding Samus captive. This time, the daemon bellowed in fury and its connection to the prey was cut. One tendril aimed itself at Tarkus and darted at him point first. Tarkus ducked, just barely avoiding the attack. He quickly realized that as long as it held a captive, it would nearly impossible to banish the creature. However, the daemon had arranged several clawed tendrils around John, preventing any sort of rescue. He pulled Samus off to one side and leaned her against a tree out of harms way while he looked for a way to finish off the warp beast. He gazed up at the tree tops where it had fixed itself and had an idea. Skirting the clearing, he found a sizable tree near the daemon. Then, bunching his muscles, he pushed. The tree groaned in protest, for its roots ran deep and strong. But few things can withstand an Astartes in full power armour, and slowly but surely, Tarkus uprooted it. Finally, gravity took hold, and the tree was ripped from the ground in a shower of earth and debris. As it fell, it struck the daemon squarely in the side and knocked it to the ground. The daemon screamed again, but this time in release. It had spent too much time in the material world without proper feeding, and as such, the ruin Tarkus visited upon its essence was too much for it to handle. The creature began to trash as though boiling before imploding in an explosion of light. Tarkus breathed a sigh of relief and offered a prayer of cleansing to the Emperor and the Primarch. Then he went about reviving the others.
John was relatively easy to resuscitate, as he awoke instantly when Tarkus touched his shoulder. "What the hell was that?" he gasped, breathless.
"That was a daemon, an unclean creature of the Warp. They are foul things, born of another world altogether, yet they feed in ours. That one in particular traps its prey with visions of glory, then drains their life essence as they fall further into the dream. My chapter's Librarians have many records of them, for they number among the most dangerous daemons." Tarkus said, he voice hard with hatred.
"So that...thing...was in my head?" John asked, his strength returning as his mind restored its integrity.
"In a manner of speaking. Daemons are born of psychic energy, so it is an easy matter for them to invade an unprotected mind. You are lucky to have survived the encounter. I trust you will be more careful next time, or you may not come back the same way you are now."
John shook his head to clear it and stood, "I don't get fooled the same way twice. Believe me, if we find another one, I'll kill it myself." he said resolutely.
"If you are truly fortunate, we will not find another." Tarkus said, "Come, let us check on Samus."
Samus was already awake when they came to her. She did not say anything when they approached, merely nodded to them solemnly. Tarkus helped her up, and John threw his arm across her shoulder to brace her.
"We should leave this place. It reeks of sorcery." Tarkus growled. "My locator tells me our destination is about half a day's walk from here. Are you fit for travel?"
Samus whispered something to John, who nodded in assent. "Good." Tarkus said, turning in the direction indicated by the flickering icon on his helmet display, "Let us be gone from here."