The Fingers
Before we could go into the Middle, we should start with going over the Fingers. The Fingers are, in essence, the Five big Syndicates which rule over the Backstreets of the City. The Thumb, Index, Middle, Ring, and Pinkie. You could say that they are the Syndicate equivalent to the Associates of the Fixers. They're dangerous folk powerful enough that not even the Wings, or the Heads would interfere with willy-nilly without a good reason. For the big part though, they keep the Backstreets relatively stable by virtue of being the only Syndicate large enough to 'govern' the other Syndicates.
The Middle
The Middle, if you try to summarize them into a quick few words, are nastily stubborn control freaks. Control, that's the one word to note. Control. You can even see it in the way they are organized: twenty-three Administrators in total, each assigned to control each twenty-three Backtreets; Managers, led by the Administrators, assigned onto each Neighborhood of the District, and Agents, led by the Managers, assigned to the Syndicates 'associated' with them, making sure that none of them go against the will of the Manager, and then the Administrator. Sharply, and tightly-dressed men and women in suits (color, and theme code dependant on the Administrator; supposedly, they have a theme they stick to every month, to keep things fun, and the people motivated) known for their masteries in various weapons, and martial arts.
Of course, their control vary from Backstreet to Backstreet, Neighborhood to Neighborhood. District 8, for example, or those within the Center North area of the City are considered to be where the Middle is strongest, as that is where their control is the most absolute. Seeing this, one might compare them to the Thumb, and while similar, they're completely different. The Thumb respects Authority in general, the Middle respects only theirs. Coincidentally, such similarity, and incongruity has made the two Fingers to often clash together, and they, oddly enough, seem to go quite well together with the Index -- though that doesn't mean they don't feud, and war against each other every now and then.
Regardless, the Middle's priority for control has made them incredibly vicious, and dangerous. Nothing goes in their control without their okay, and this 'okay' depends on the culture that the Administrator, and the Managers cultivate over their control, and they would do anything to assert, and gain control. Anything. Kill, murder, torture, mutilate, and so many countless horrifying acts -- they'd do each and every one of them willingly, one-upping one act and another, grinning or stoically, if it means they would gain control.
Supposedly, their Iron Fist Tyranny over the Backstreets make things fairly stable. Not peaceful, or non-violent, but stable -- predictable, and expected. Static, so to speak. Of course, tyranny is still tyranny, and that 'fairly stable' state could change anytime on the whim of the Administrator, Manager, and Agent. If an Agent one day decides on a whimsy that the Syndicate they're attached to is not 'up to standard', then there's nothing that Syndicate could do. Similarly, if a Manager decides that the neighborhood they're controlling should have every pregnant woman killed... and if the Administrator of that Backstreet decides on a whim that... well, you get the idea.
But what happens when they lost control? Well, they'd do anything -- no, they'd do the most extreme, most destructive, most poignant course of actions to establish said lost control back. They are stubborn, insanely so, in a way that can be compared to the Index's obsession to the Prescript, and the Thumb's obeyance to their own Structure -- only, the Middle does not have such a thing to depend on. They stand above all else, thus they only have themselves to follow and rely on.
... Even if it means razing everything down to the ground, even if it means all that's left to control is only ashes and nothing else, so long as they have that control back, they'd do it with a laugh.