The thief's gamble - Juliet E. McKenna

In Einarinn, the secret of magic is known only by an elite few. They live in deliberate isolation, under the watchful eye of the Archmage. But nothing last for ever.

Livak is a part-time thief and a full-time gambler, long accustomed to living by her wits and narrowly avoiding serious trouble. When she attempts to sell a stolen antique to a passing merchant, she finds herself pulled into a new and dangerous world of political intrigue in which the stakes are higher than anyone involved can imagine.

For the antique she has acquired dates from a particular period in the history of Einarrin about which little is known, but much has been speculated. And when the truth begins to emerge, Livak decides to take the greatest gamble of her life.