Lair (1979)
Lair by James Herbert

They've waited long enough.

The mutant white rats had grown and mated, creating offspring in its own image. They dominated the others, the dark-furred ones, who foraged for food and brought it back to the lair.

Now the dark rats were restless, tormented by a craving they could not satisfy. But the white sluglike thing that ruled them knew. Its two heads weaved to and fro and a stickiness drooled from its mouth as it remembered the taste of human flesh.

Quotes...

James Herbert “Many people believe that a follow-up to a previous book never creates the same excitement – but here’s a sequel that breaks the rule, such is the tension generated by the famous Herbert rats… If you thought highly of The Rats, then rest assured you’ll want to hear about Lair.”

- from Bookshop, June 14, 1979