The Mystery purview allows Scions to scan the web of Fate.
Unlike all other purviews except Modèle:L, Mystery has no Boons. Instead, a Scion may use the Mystery purview to tap directly into cosmic awareness, gaining knowledge by sensing the interconnectedness of all things within the web of Fate. A Scion with the Mystery purview records it as a dot value from one to ten, and increases it by buying new dots as if they were regular Boons, with the same costs and prerequisites. A Legend 12 Scion with ten dots of Mystery can learn its Avatar, the Wyrd.
Once per story per dot of Mystery she possesses, a Scion may spend one Legend to roll (Intelligence + Mystery), adding no automatic successes from Epic Intelligence to this roll. She may then ask the Storyteller one question per success scored on this roll, which the Storyteller must answer truthfully and directly (if somewhat tersely). Because Mystery examines the parts of the tapestry of Fate that have already been woven, these questions and answers can address the present and the past, but may never glimpse the future-- the strands that have not yet been woven into Fate's design.
For the remainder of the scene, the Scion becomes the Wyrd, Fate's direct agent. Surrendering completely to the ebb and flow of Fate, the Wyrd moves in mysterious ways, taking actions that may seem insignificant or inscrutable, even to the Wyrd itself. Like the flapping of a butterfly's wings, though, the Wyrd's smallest impulse has far-reaching consequences-- all a part of Fate's ultimate design.
In game terms, when a Scion becomes the Wyrd, the Storyteller controls that character for the remainder of the scene, so that the Wyrd can be doing whatever the ST knows needs to be done. The Scion's player benefits because the Wyrd neatly resolves some messy plotline important to the Scion, and the ST benefits because the Wyrd's actions can be used to set the wheels of future plots in motion.