To Green Angel Tower is the third and final novel in Tad Williams' Memory, Sorrow, and Thorn trilogy. Due to the length of the novel, the paperback version had to be split into two separate volumes, known as To Green Angel Tower: Part 1 and Part 2. In the United Kingdom, the two paperback volumes were titled To Green Angel Tower: Siege and To Green Angel Tower: Storm. The saga follows a young man named Simon as he is caught up in an epic adventure.
The story begins with the forces of Prince Josua Lackhand rallied at the Stone of Farewell, where the icy hand of the Storm King Ineluki has yet to take a deathgrip on the land. The remaining members of the League of the Scroll have also gathered at the Stone in hopes of unraveling an ancient prophecy. If deciphered, it could reveal to Josua and his army the only means of striking down the unslayable Storm King.
After Simon and Binabik have their reunion, they come to the realization that Memory - one of the three Great Swords recognized as being key to defeating the Storm King - is one and the same with Bright-Nail, old King John’s sword that was buried with him not three years previously. The trouble is, the grave of King John Presbyter lies in the shadow of the Hayholt, the stronghold of King Elias, and between the Stone of Tears and Hayholt marches the army Elias has sent to besiege the defenders.
Meanwhile, Miriamele, Elias’s daughter who has joined Josua’s cause, is an unhappy prisoner on the ship of a lascivious and ambitious lordling. Another princess, Maegwin of Hernystir, falls deeper into madness, leading her people in a seemingly futile resistance against Elias’s allies who have conquered her kingdom, and deep in the ancient forest of Aldheorte, the immortal Sithi are mustering for a final conflict.
While Josua and his army must make a final stand to try to delay the forces of King Elias, Simon embarks upon a quest to Hayholt to try to obtain the last of the three legendary swords and use their hidden magics to defeat The Storm King Ineluki and restore peace to Osten Ard once and for all.