The Spell of the Black Dagger — Lawrence Watt-Evans

Tabaea was an ordinary thief, sneaking and prowling and stealing for a living. Then one night while burgling a house, she witnessed a wizard teaching his apprentice a spell -- the creation of a magic dagger.

Tabaea decided to try the magic for herself. But even though she could feel the power rising around her as she went through the steps of the ritual, something had clearly gone wrong. The apprentice's dagger had glowed; it had resisted attempts to pick it up; and there had been a blinding flash at the end of the ceremony.

But Tabaea's dagger didn't do any of those things. And it wouldn't free her from bonds, or heal her wounds -- it didn't seem to be magical at all. It just turned black.

Then, by chance, Tabaea discovered that her dagger indeed had its own kind of unusal magic -- a dark, powerful magic that promised invincibility to its bearer.

But magic can be dangerous even in the hands of an expert -- and for Tabaea, magic and power could spell disaster . . .