In 1580-1581, the Austrian Habsburg ambassador to the Ottoman court shared news of a remarkable letter and self-portrait that had arrived from an Ottoman subject in Habsburg captivity. Tracing the scramble for details on the matter and its import for Habsburg-Ottoman diplomacy reveals the structure, contours, and challenges of the Habsburg mission in Constantinople. The article argues that the image and the accompanying letter may be a forgery seeking to place the ambassador and the peace he was to uphold in jeopardy. Instead, the ambassador himself was captive to the factions, rivalries, and shifting loyalties in the borderlands that played out in the diplomatic culture of Ottoman Constantinople. This reveals the possibilities, limits, and ranges of control that early modern resident ambassadors had of their missions.