“I am nought but a blade of the Emperor”
The Acolytes briefly ran into the Callidus Assassin calling herself operative Gamma prior to their meeting with Inquisitor Set on the forbidden isles, albeit at the time she was disguised as an old ‘pensioner’ (an odd Aventinian custom where people of a certain age ‘retire’ and are paid a small ‘pension’ by the planetary government). While the Acolytes met Set (and were betrayed), Gamma interrogated both the ex-IG veteran Lament and the mercenary Steve (not related to the other Steves) and left Steve badly traumatized. She also left a message to the Acolytes telling them to come meet her on the Witch Isles, but the Acolytes ignored the request and left for the Isle of the Rose instead.
So far, the Acolytes know nothing about her goals on the planet, or about her current whereabouts post-blood sky.