Prologue:
A successful experiment.

The Expediter listened in silence. With difficulty, it managed to remain motionless. The Expediter was in the middle of its sex-interphase and the hormonal changes always made it irritable. That irritability interfered with its logical thought processes. The Expediter did not want to act out of simple aggravation.

Should it continue to prevaricate? 

Lying was possible, of course, especially to such as these. Primitive creatures, really, the female as much as the male. But the Expediter thought that it would still be very difficult. Any explanation as to why the starship had left so hastily would seem contrived—even to the two stupid beings who were bombarding the Expediter with their clamor.

The Expediter pondered the matter for some time before coming to its conclusion.

No. Further prevarication would hardly be worth the effort. Besides, the Expediter thought that it was time to discover how well the protease haemato-toxin affected this species.

The dart-spines targeted, ocelli orientating them to center on the soft, bulging midriff-masses. The two beings in the room made no attempt to escape. They simply continued their babble. Apparently, they did not recognize the purpose of the spines. An interesting datum.

Razor-tipped, barbed harpoon-darts streaked out, each trailing their protoplasm hose. The skewering force of the darts cut into the gold head-filamented female in mid-shrill. Her bleat became a scream as the Expediter's internal myomeres pumped the massive dose of digestive-toxin into the soft-bodies.

The creatures threshed. The Expediter studied the ensuing process with interest.

Cell-lysis caused the circulatory fluids to pour out of the eating and scent-detection orifices. The soft, pallid epidermis ulcerated and erupted, spraying liquefied flesh. The bipedal beings were now twisting and writhing in bizarre contortions.

Another interesting datum. The Expediter had not realized that their vertebral columns could bend as far as that. Endoskeletons were strange biological adaptations. It made a note of that flexibility.

The Expediter watched as lysis continued. A full two minutes passed before the bodies finally lay still. Also worth noting. The digestive-toxin was not rapid, but it was effective. That, of course, was to be expected. The Overphyle had yet to discover a sentient species immune to it.

The Expediter disengaged the barbs of its harpoon darts, pulled them out and winched them back into itself. Then, after a moment's hesitation, decided not to feed. It was not particularly hungry, and there was always a slight risk with ingesting untested alien protein.

Multiple ocelli checked the room. Other than the two sprawled, bloody, ruined bodies there were no signs of the Expediter's passage.

Calmly, it left, locking the door behind it. In the silent and luxuriously appointed room, the only trace that remained of the murderer's identity was a faint camphor-naphthalene scent. That would dissipate within a few minutes. The Expediter itself was quite oblivious to the smell, but it hardly mattered. By the time the servants found the bodies, the odor would be indistinguishable from the general reek.