by Mercedes Lackey
CompleteAll books have been published
Tarma, a Shin'a'in swordswoman, and Kethry, a sorceress bound to a magical sword, swear blood-sisterhood and set out as mercenaries. Set mostly beyond Valdemar's borders, a couple of generations before Arrows of the Queen.
The Oathbound
1988
Oathbreakers
1989
Oathblood
1998