From the introduction:
Weak and unfamiliar with its surroundings, it holes up and eats what garbage it can. It grows quickly and as it matures it soon begins to hunt rats and other vermin. Sewer workers first begin to notice signs of the thing, but pay it no mind. As these occurrences grow, they soon begin joking about "something on the loose." Plentiful as they may be, rats and garbage cannot sustain the thing's energy requirements. By now it has grown to the size of a large cat. It leaves the sewers to forage for new food sources. Utilising the night it begins to prey on cats and dogs often leaving carcasses which are found the morning after. Concern grows over the presence of a rabid animal. The joke of "something down here" begins to grow thin as some sewer workers are genuinely spooked by something. They hear things; see things; find fragments of sloughed off skin or large patches of blood. As pet slayings continue public concern grows. Animal control begins to search for the creature, but it remains elusive. The odd partial animal print is recovered, but it cannot be identified with any degree of certainty. Officials deny that there has been an escape from the zoo. A woman is later interviewed on the news about having narrowly colliding with the suspected rabid animal as she drove home in the wee small hours. As she hit the brakes it jumped up and clattered over the roof of her car, scraping the paint work extensively. She gives a mistaken description of it as being like a large muscular dog, dark in colour.