Mordant's Need is a fantasy two-part book series by American writer Stephen R. Donaldson, comprising the novels The Mirror of Her Dreams (1986) and A Man Rides Through (1987).

Terisa Morgan opens the series living a vacant life, supported by her father from afar and volunteering at a mission for lack of anything more purposeful to do with her time.

As mirrors are inextricably linked with magic in Mordant, Terisa's home decor convinces him that he has stumbled into the lair of a powerful sorceress.

He persuades her to accompany him back to the snowbound castle of Orison, where she finds herself embroiled in a morass of intrigue and danger from both the political plotting of a corrupt court and from the frightening magical creatures that appear without warning and can't seem to be defended against.

The mysterious rogue Imager is still sending magical creatures to cause destruction seemingly without rhyme or reason; the High King's Monomach, the best swordsmen in the land, appears in Orison by seemingly impossible translations; and Geraden remains firmly convinced that he has not made a mistake and that Terisa definitely is to be Mordant's champion and salvation despite her own doubts, protests, and debilitating passivity.