Men visiting an alien world encounter a great cat-like being, Coeurl, a survivor of a dead culture who has killed nearly every living thing on his world in search of phosphorus--the one thing required by the otherwise-immortal being.

Coeurl, pretending to be harmless, kills a number of the visitors, but fails to evade suspicion. When the men aim to kill him, he launches their ship into space, barricades himself in the machine shop, and builds a small duplicate ship for himself, with an eye toward taking this technology back to his world and launching his species on a galaxy-conquering spree.

However, his lack of true understanding of the technology is his undoing. Terrified by the unnatural behavior of the anti-accelerators, he kills himself rather than be destroyed by the humans.

Finally, the humans plan to lure in all of his species, to kill them all in order to remove them as a threat.

Notes

Coeurl can sense and manipulate electromagnetic waves, among other things. He can control electrical devices and use electricity to reinforce or destroy metal. He communicates, too, through radio waves, and senses the 'vibration' of the phosphorus, which he calls 'id', within the humans.

There's a small bit of misdirection in the beginning of the story. Coeurl calls phosphorus 'id' and it seems likely that it means something else, but then the term 'ego' is used early on, probably just so as to confuse the issue.

The story is basically a tale of suspense. The scifi trappings aside, you could tell nearly the same story with a bunch of sailors landing on an island with a murderous inhabitant.