 The siblings' arrival is the catalyst for a climactic battle between the Railwaymen and the Canallers.Widgie manages to escape and rescues Jen, and the realisation of the threat they pose should they escape aboveground and expose the System forces the Railwaymen and the Canallers to set aside their differences for the time being, to collaborate in an effort to recapture them.In the course of the battle giant rats, kept imprisoned in a blocked-up tunnel, are released and proceed to spread through the whole system.