A nameless mouse washes up on the western shores of the lands near Mossflower, a refugee from a pirate island across the ocean. She rediscovers her past and identity as Mariel, daughter of Joseph the Bellmaker, and seeks to exact her revenge on the tyrant who has ruined her life. With the aid of friends from Redwall, Mariel leads the way across the seas to the island she once called home, while Redwall is once more under siege...