This isn't the actual story it's just the main idea
Young squirrel found on doorstep of redwall with two things: a battleaxe and a map.
A nomadic Clan of badgers on an island who are subject to the stealing if their children by giant bilge rats.
On the same island a Confederation of squirrels is without a king for the fist time in a long time. The confederation has more than fifty nations of squirrels including regular brown squirrel, Fox Squirrels, gray squirrels, red squirrels, and black squirrels.
When the young squirrel grows up he finds out his destiny is to become king of the squirrels on the island via a dream from Martin. A mouse distantly related to Matthias the Warrior joins him, along with the newly appointed Log-a-log and a stow away child otter who has a great admiration for the matthias relative, plus Foremole's son.
A baby badger is captured and is beaten to death. A slightly older badger witnesses and vows revenge. (SPOILER: This badger becomes Badger lord of Salamandastron)
The rats accidentally stumble upon some squirrels from the Confed and skirmish with them. The rats win but some of the squirrels escape. The survivors return to the steward of the confed and the nations are split and begin to war amognst eachother due to the accidental killing by a young black squirrel to a respected fox squirrel elder.
The young king to be, Log-a-log, and Champion of Redwall journey to Salamandastron and find it without a leader. Many hares volunteer to go but only one is allowed, but he has other plans and wishes to rule the mountain himself (EVIL HARE??)(Yes). The hare ends up killing either the champion or logalog (don't know yet) and has to deal with the soon to be king. He gets his ears and foot chopped off as punishment.
While there is a full scale war between the nations, the rats, and the badgers, the king arrives and unites the squirrels against the rats. The badgers also find their young hiding with one of the tribes of the flying squirrel nation and attack. The badger's leader fights with the squirrel king and later peace is resolved.
While all this is going on, Redwall is facing an assault from weasels and ferrets.