Don't Ask Succubus

Two witches, young impulsive Aurora and cold precise Erica, had to call succubus for finding "Stone of Shadows", the powerful artifact, which helps to free Erica's former partner from Interworld. But the cunning succubus has completely different plans.
Especially about Aurora.
The succubus is enclosed in circle and cannot use magic - unless she provokes witches to use their power. Each use of magic near the circle gradually destroys its defense.