Amberley Vail is a member of the Ordo Xenos of the Inquisition and the lover of Commissar Ciaphas Cain, HERO OF THE IMPERIUM! Unique among the members of the Inquisition, she not only displays sanity, but also self-awareness of just how off their rocker everyone else in the Inquisition can be. She goes about the galaxy fighting aliens with a quip and perky sense of humour. But don't let her light air fool you, as she can be as deadly as her position demands. She was the one who realized that Jurgen was a blank, after her sanctioned psyker Rakel had an extreme reaction to physical contact with him. She would later go on to edit the Cain Archives, detail Cain's private memoirs for use by the Inquisition (after we assume his death given his Admissions in these). Her edits consist of inserting a few other sources of relevant information to provide perspective, and a large number of footnotes whenever she feels she needs to elaborate on something or make additional commentary. As often as not, she just uses them as an excuse to take jabs at the Radicals and members of the Ordo Malleus or defend her vanity when it is implied she ate too much (only once). Whenever the Cain archive goes into times before he met her, she also is prone to insulting (either directly or indirectly) Cain's prior paramours, and may edit out any family-unfriendly information regarding his liaisons with her and others.
She tends to take a light-handed approach to executing her Inquisitorial duties, often simply arranging to have the appropriate people in the appropriate places at the right time to make a difference. Cain and Jurgen often end up crossing paths with her when she makes sure their regiment is the one to arrive at a conflict that calls for their talents. However, she is also comfortable getting stuck in when need be, and owns a set of ornate power armor that (according to Cain) would make a Techmarine jealous. Apparently, she is pretty good at purging Genestealer nests with it.
As expected for an Ordo Xenos Inquisitor, she knows a few non-human languages. She is functionally conversant in Tau, knows a little Eldar, and is fully fluent in Orkish (though she admits that is not hard since Orkish apparently consists mainly of a few guttural bellows and smacks to the head for emphasis.)