In the Battle of Osis, the concluding volume of the Osis Fantasy Trilogy, Jonathan and Magenta's adventure begins in Ottawa on a bitter-cold winter's night. Summoned by Master Cobalt to the Rideau Falls, they venture beyond the frozen water into an ice palace - a secret meeting place for the Master and his young friends. Here, Jonathan and Magenta learn the true origin of the evil Black Pearl of Osis and the identity of its Guardian, Mistress Ebony, ruler of the City of Osis. But, rumour has it that Mistress Ebony has broken her vow to guard the Black Pearl from falling into cruel hands. Sinister forces begin to assemble across the land, threatening to ruin all life. Before they confront the enemy in a final attempt to destroy the Black Pearl of Osis, Jonathan and Magenta must go on a dangerous mission further back into the past in search of the magic sword Anagallis and convince its peace-loving owner to join their ranks in a deadly battle. The Battle of Osis is a tale of mystery and suspense, betrayal and revenge, love and loss, temptations and disappointments, jealousy and greed, but also a tale of growing wiser, of friendship, loyalty, valour and forgiveness.