Cobwebs of Pearl. The Occasion Mists, #4

(The Occasion Mists - Hint 4)Imprisoned; no one can feel your pains but you!Heart, an ancient city that holds the occupants of descendants of Earth and Alien beasts is on a constant vigil, always watching for signs of an alien invasion. Brought together as a group, and whose 'soul' purpose is to protect the Earth itself, the dwellers of Heart are only slightly suspicious about an inward bound comet heading towards the Earth from a dark region of the Kuiper Belt.
As a precaution, one of the dwellers of Heart is dispatched to Earth to check up on the arrival of the comet. However, because they expect no trouble, the Heart Dweller is expected to use their time on Earth as a holiday; a chance to familiarize themselves with current affairs, styles and language, should they need to work covertly on the Earth in the near future. No sooner has the Heart Dweller arrived on Earth when any idea of a holiday is forgotten.
A huge spider stalks the cities of Earth, living on fresh human prey, whilst seeking out pieces of rock that have fallen from outer space. Wherever the spider goes then so does its humanoid captive, a powerful visitor from Heart whose own mighty powers have been quelled by the new powers and intelligence of the mutated spider. The spider keeps the captive alive only because, with the right kind of union, the spider could benefit from the powers of the visitor from Heart and, combined with the powers from the strange comet fragments, the spider could rise to be the most intelligent and powerful evil to have walked the Earth.
Two forms of intelligence are in a battle to the bitter end; an end which might leave one of them still alive, or maybe none.