A specialised arm of the Vaticine Church formed by the Third Prophet and tasked with seeking out heretics and enemies. Originally they acted as a police force but over time their power grew with torture first becoming a rare exception and then eventually becoming the norm.
Scientific research walked a line very close to heretical questioning and as such was never favoured by the Inquistion, the Hierophants had always supported it however and thus they could take only small secretive actions bending rules and permissions where they could. When the last Hierophant died and the Cardinals went the Inquisition found itself answerable to no one and their power and influence grew rapidly to spread across all of Theah.
With the election of both a new Grand High Inquisitor and a new Hierophant the Inquisition has changed drastically, officially the Church once again supports 'suitable' scientific research and once more they have a higher power to answer to. Only time will tell what this means for the Inquisition.