Enraged and embittered, Armus has waited alone for eons on his desolate homeworld, malevolently searching the heavens for a means of ending his solitary exile.  When he spies an approaching alien shuttlecraft, he snares it with a force field, bringing into his grasp two officers from the Galaxy-class Federation starship U.S.S. Enterprise, one of whom is an empathic half-Betazoid woman, Counselor Deanna Troi.  But Armus cannot rejoice at receiving visitors, his first since the Vagrans discarded him so long ago; lacking any moral sense, Armus is capable only of tormenting them.

When an Enterprise away team arrives on Vagra II to recover the missing crewmembers, Armus bars its path, first taking the form of a flowing oil slick, then rising into an imposing, slime-covered humanoid shape.  When one of the officers, Lieutenant Natasha Yar, attempts to reach the shuttlecraft, he kills her with a blast of energy -- an act which Armus is disappointed to discover gives him no satisfaction.  Nor does he derive any enjoyment from his subsequent torment of Troi, whom he keeps trapped in her shuttle, incommunicado behind an impenetrable force field.  Armus is frustrated by Troi's refusal to despair, despite his taunts that her friends have abandoned her, just as his own creators had forsaken him.  Receiving only her pity from her, Armus flies into a blind rage, which weakens his force fields.

But it is Captain Jean-Luc Picard who perceives and exploits Armus' prime vulnerability: The immortal creature is terrified of being left alone, forever immune from the release of death.  When Picard forces Armus to face this, the resulting emotional trauma further degrades Armus' force fields, enabling the enterprise to beam the captives to freedom.  The starship leaves Armus alone once again, with fear, rage, and hatred as his only companions.