Isabeau was 5 feet 3 inches (1.6 meters) tall, slim but with a bountiful chest and wide hips. When she wore her dark, shaggy hair long, it stretched down past her knees, though it was just barely past her shoulders when she worked as a tavern wench. She had a hook nose, large dark eyes, full lips and light brown skin. Isabeau had a scar on her thigh made by her mother when Isabeau was a baby just in case Lucia ever decided that she needed to find her daughter.
Isabeau made sure that she wore clothes and accessories that showed off her body: tightly fitting bodices, low-cut gowns, and necklaces that drew the eye to her breast were the norm while living in Waterdeep, all accentuated with jewels. In her former life, she used similar tactics with whatever simple clothes she had.
Isabeau was still an infant when the Ten Black Days of Eleint forced her mother, Lucia Thione to flee for Waterdeep before an angry mob could murder her for her connection to the Tethyrian royal family. Lucia abandoned her illegitimate daughter at the Friendly Arm Inn.
Isabeau was raised by Bentley and Gellana Mirrorshade, who gave her the name Sophie and told her when she was older that she owed them a debt for the expense of raising her (though in reality, the kindly gnomes were just trying to keep her safe in their fortified home for as long as possible). She worked as a kitchen maid and later, as a tavern wench for her foster parents, and never could pay off her supposed debt.
A wandering thief took a liking to Sophie and taught her his trade, a favor she repaid by stealing all of his lockpicks and tools.
One fateful night in the Year of the Banner, 1368 DR, Sophie discovered her true heritage while speaking to a mercenary working for Elaith Craulnober, who wanted to ransom her to the highest bidder back in Tethyr. Angry at Bentley for lying, frustrated by her life, and fearful of what Craulnober would do to her, Sophie left the Friendly Arms and was met by Arilyn Moonblade, who escorted her to Waterdeep where Isabeau Thione claimed what was left of her mother's Waterdhavian estate.
Isabeau was a natural-born thief. She loved the challenge of a prize as much as the item itself and the thought of her first theft still filled her with pride. An ambitious woman, Isabeau was self-centered and always looked to improve her lot in life. She made sure to make herself the center of attention and was an expert flirt. She also knew how to use a knife when she needed to.
One thing Bentley Mirrorshade managed to drill into her, however, was the so-called "Mirrorshade Cipher" — "The treasure worth keeping, the risk worth taking." — intended to be a lesson on how to weigh risks against rewards.
Isabeau left the Friendly Arms with only the clothes on her back and her thieves' tools. Once she got to Waterdeep, she inherited everything her mother had to leave behind there.