Alright, so the big twist in 'The Rats'—at least the James Herbert one—isn't some secret identity or hidden mastermind. It's the sheer escalation. You start off thinking it's a standard monster-of-the-week deal, just bigger vermin in the London sewers, right? But the reveal is that they're not just mutated by random chemicals; they're an active, adaptive plague spreading out of control, and the government's response crumbles in real time. The 'twist' is more of a tonal gut-punch. It becomes clear nobody's safe, the heroes aren't special, and the ending is basically just surviving the first wave with the horrifying knowledge that it's just the beginning. The real horror is realizing the rats are winning because society's infrastructure is so fragile.
What got me was the bleakness of it. There's no clever solution, no magic poison. It feels less like a twist and more like the floor giving way. Herbert pulls the rug out by making the threat utterly mundane in origin but evolutionary in its success. You expect a big showdown in a lab; you get a desperate, messy retreat. The final pages leave you with this dread that containment has already failed. Classic 70s horror, really. No comfort, just teeth.