Slayers appear to be man-sized humanoids dressed in demonic looking plate armour. This armour is actually a bio-mechanical suit for the true form of the creature, a small squid-like alien. However, the armour is treated as an extension of the Slayer and any damage to the armour causes damage to the creature. The body armour is slow and ponderous, always striking last in melee combat. For distance travel, Slayers will often ride normal horses, though they always dismount to fight.
Slayers carry only one weapon of alien design: the Slay-Spear. The weapon can fire a blue pulse of energy and has a two-shot capacity. Once all shots have been fired, the weapon can be reversed to use as a two-handed spear in melee combat.
Slayers hail from another planet and are alien to the planet Krull. They are immune to any kind of magic. Their senses are equal to human and they have no ability to see in darkness without a light source. They will not communicate and cannot be reasoned with or bribed; their loyalty is only to the Beast of the Black Fortress. If killed, a Slayer gives off a keening shriek and will abandon its armour, burrowing into the ground, never to be seen again.
Prince Colwyn and his allies who were on a mission to rescue his bride Princess Lyssa, use captured Fire-mares (the only transport fast enough to reach the teleporting fortress in the same day) to reach the Black Fortress, but are attacked by Slayers, who kill Rhun. When they get to the Black Fortress, Rell uses his massive strength to hold open the huge doors long enough for the others to enter. He dies when the entrance closes, crushing him. Kegan is killed by a Slayer shortly afterwards and Colwyn gets lost in the labyrinthine interior. When the Slayers try to kill Titch, Ergo magically transforms into a tiger and kills the Slayers, injuring himself while saving Titch's life. Torquil and Oswyn are caught in a trap with slowly closing walls studded with massive spikes.
Colwyn injures the Beast with the Glaive and finds Lyssa. He is unable to recover the Glaive from the Beast's body. Lyssa realizes that her ability to project flame can finish the beast. The two use the flame to slay the Beast and they make their way out of the crumbling Fortress, finding Torquil and Oswyn and retrieving Ergo and Titch. Colwyn uses the fire to blast his way out of the Fortress, which collapses and disappears. The Beast and his army of Slayers were no more.