This book starts the two book series entitled Mordant's Need.

Terisa is a woman who has a very droll life.  She lives in an apartment paid for by her unloving father.  She works for Father Thatcher at a mission as a secretary.  She has decorated her rooms with mirrors so that she can prove to herself that she exists.  She has this problem because of the way that she was treated as a child by her parents.  She was often times locking into dark closets for punishment.  Her father never wanted her and her mother just went along with what the father wanted.

One day a man enters her apartment through one of the mirrors and persuades her to follow him.  She does and finds herself in another world.  A world where mirrors do not reflect what is in front of them but other worlds and places.  Gereden, the man that translated her into this world, is an Apt of the Congery.  This is a group of people that can fashion mirrors and use them to send or bring things through them.

Gereden was supposed to bring through a champion from his mirror.  He brought forth Terisa instead which is supposed to be impossible.  His ineptness is blamed and, since he is the oldest Apt-never-to-become-an-Imager in history, this is believed to be the case.

Terisa is given into Gereden's hands for safe keeping but he is told not to answer her questions.  He takes her to King Joyse, the ruler of Mordant, were she also meets Adept Havelock, a mad Imager.  King Joyse and Adept Havelock are playing hop-board (or checkers) and they both appear to be somewhat crazy.  King Joyse has been neglecting the kingdom and appears to have no interest in what is happening other that hop-board.  Adept Havelock has been mad since he went through a flat mirror (something the Imagers cannot do with destroying their minds) in pursuit of an old enemy.

Terisa is later shown to her rooms where a secret passage admits Adept Havelock.  He takes her to his rooms where Master Quillon, an Imager, explains the history of Mordant to her (against the Congery and King Joyse's orders).  When Terisa gets back to her rooms, a man is there fighting with the two guards that Gereden had asked to protect her.  She is saved by Havelock when he uses a mirror that shows a sun to temporarily blind the attacker.

Terisa finds herself liking Gereden but she also feels strangely drawn to Master Eremis of the Congery.  She begins to feel that he has answers that will save Mordant and he also has a sort of power over her that compels her to him. 

Master Eremis calls a meeting of the lords of Mordant, the Prince of Alend (an enemy of Mordant) and the Congery.  This falls apart with the eventual results that the Alend Monarch sides with Elega, King Joyse's daughter, to lay siege on Orison.  Also it provides the impetus for the Congery to attempt to force-translate their champion. 

After the champion is translated, he blows a hole in the side of Orison and escapes.  Later, Myste, a daughter of King Joyse, uses the secret passage in Terisa's apartments to go to help the champion after causing Terisa to swear to silence about her actions.

After several event and plots and schemes, it comes to pass that Gereden, Terisa, Castellan Lebbick and the Congery are gathered to hear the details of Master Eremis' accusations against Gereden and vice versa.  Gereden's brother Nyle is there to support Master Eremis in the matter but he asks to talk with Gereden in private first.  When they meet, Nyle falls from an apparent attack from Gereden.  Gereden flees and Terisa follows after him.  They meet in the room with Gereden's mirror that translated Terisa.  Gereden goes through the mirror but does not appear in the image afterwards.  Terisa is then captured by Castellan Lebbick. 

This ends the first book of Mordant's Need.