"He plans to grasp some sort of dirt on the captain and then get complete control of the over the order"
Ah yes, plans that hinge on blackmail material you haven't yet discovered and may not exist. Brilliant.
Unfortunately a fairly typical blackmail scheme relies on first arranging the dirt, which will then to be used later in blackmailing. The same people may first bribe someone and then use the evidence, which obviously will be easily available for the blackmailer, against the target. Or arrange an illicit affair for the target and record it all. Neither of these basic ones would work against the virtuous captain, but I'm sure that scumbag noble, while lacking brains himself, can order much more skillful experts to handle it, one way or another. I'm not in that sort of business, so my ability to come up with examples is limited. But since it's an underdeveloped fantasy world, it will be probably something straightforward since they don't actually have cameras for recording stuff.