Momentum is right! This piece was great for demonstrating that. The tension starts ratcheting up almost immediately. It reminds me of the beginning of a roller-coaster ride, where you're being pulled up to the top of the first hill. You've got this mix of excitement and dread that peaks right when you teeter on the edge, and then the rush of the ride - which is sudden and over before you know it. I think it's an apt analogy for this piece you've got here.
As far as constructive criticism, I think some of the action might be a little unclear and hard to follow. That's partly because you're seeing it through the eyes of the narrator, who's stationed out of the action on the balcony. To some extent, the confusion adds to the tension of the story, so the lack of clarity can actually be an asset if you're looking to elicit a certain response in a reader - and it's something you definitely accomplish here.
Thanks @beowulfoflegend, that's really nice feedback. So, yeah, confusion is kind of the effect I was going for. I wanted the reader to have that feeling of being stuck, the whole time, in the room with the main character as he watched his carefully laid plan come apart.
But, at the same time, that's a bit of a cop-out because I find it much easier to write a 'this is confusing' scene than a scene where exciting stuff is happening, but you still know exactly what's going on. In general, I just think it's hard to convey lots of information, quickly, without overloading the senses. If you think of action movies now, it's hardly ever possible to see what's going on, but that confusion just gets covered up with a lot of pyrotechnics. That's what made Mad Max: Fury Road such a masterpiece: so much going on, and you knew what was happening all the time. It was incredible, and I guess that's the model I'd aspire to when writing an action sequence - it will take a lot of practice, though.