The Stone Duology Series by Victoria Strauss

Sixteen-year-old Alexina, estranged from society by her unrealized extrasensory powers, rescues Taryn, a teenager from the parallel world of mindpower, who awakens Alexina’s long-hidden gift. Awed by the discovery of her psychic ability and hoping to belong at last, Alexina eagerly joins Taryn and his companions in their Quest to recover the living Stone, the heart of the mindpower world stolen by a renegade from their universe... moreSixteen-year-old Alexina, estranged from society by her unrealized extrasensory powers, rescues Taryn, a teenager from the parallel world of mindpower, who awakens Alexina’s long-hidden gift. Awed by the discovery of her psychic ability and hoping to belong at last, Alexina eagerly joins Taryn and his companions in their Quest to recover the living Stone, the heart of the mindpower world stolen by a renegade from their universe.The search leads them deep into the wilderness, to an enchanted palace surrounded by thorns. There the thief waits, a being of incalculable strength who calls to Alexina with a power she cannot deny, and a promise she does not understand.In the battle that follows, good and evil become indistinguishable, and Alexina learns that friendship does not always guard against betrayal. less

(from inside jacket) "In The Arm of the Stone, Victoria Strauss has created a reality of two worlds: Handpower, based on technology, and Mindpower, in which tools are regarded as dangerous heresy. A thousand years ago, when the worlds split apart, an ambitious sorcerer seized the Stone from which the powers of mind are drawn... more(from inside jacket) "In The Arm of the Stone, Victoria Strauss has created a reality of two worlds: Handpower, based on technology, and Mindpower, in which tools are regarded as dangerous heresy. A thousand years ago, when the worlds split apart, an ambitious sorcerer seized the Stone from which the powers of mind are drawn. To keep the new world from contamination, he established rigid rules circumscribing which machines may be built and what types of knowledge may be pursued-rules brutally enforced by an order of Guardians known as the Arm of the Stone. . . ." less

At the heart of the fortress lay the Garden. At the heart of the Garden lay the Stone. -- a living entity of power beyond understanding. Then came Bron, his arrival long foretold as the one who would restore the balance to a world torn asunder centuries ago. But Bron had other plans. He stole the Stone...and vanished.Now Bron's daughter Cariad, a skilled empath and assassin, must follow the footsteps of a father she's never known into the depths of the same fortress... moreAt the heart of the fortress lay the Garden. At the heart of the Garden lay the Stone. -- a living entity of power beyond understanding. Then came Bron, his arrival long foretold as the one who would restore the balance to a world torn asunder centuries ago. But Bron had other plans. He stole the Stone...and vanished.Now Bron's daughter Cariad, a skilled empath and assassin, must follow the footsteps of a father she's never known into the depths of the same fortress. Waiting there is Jolyon, her father's greatest enemy, a man whose thirst for domination is matched only by his taste for blood. Cariad must learn the secret of Jolyon's strength before it is too late. For just as her father's arrival was prophesied, so too is his return. less