As Redwall slumbers in the summer sun, it is unaware that the mountain stronghold of Salamandastron lies besieged by the weasel army of Ferahgo the Assassin, and that the deadly Dryditch fever is creeping towards the Abbey. But the sword of Martin the Warrior sends Samkin and Arula from Redwall over forest, swamp and great waters to try and save Salamandastron from being turned into a centre of evil power..