You wish you could step out of this suit. Step out of this goddamn heat trapping nightmare. Yet you know this is the only thing that's keeping your enemy from recognizing you. You put up with the lack of clean air and the heavy weight of the unfamiliar weapon, because you have a job to do. You were sent here to neutralize the enemy's automated defences, knowing that your failure means your death, and possibly the death of your entire team.
You quickly find the first sentry that was set up, and discover, to your horror, an engineer guarding it. You have to plan this carefully. You have to hope that the engineer won't have time to call for help before you can take down that sentry.
His back is now turned, and you strike. You cover his mouth with your glove and a slash to the throat with your knife, and there is no more resistance. However, the sentry, the nasty little bugger, slowly whirls towards you, signifying it somehow recognized your deception. You quickly hook up your electro-sapper onto the sentry gun, and then slowly drag the engineer's body away.
You now have another disguise to use. You quickly strip yourself of the asbestos lined suit, and change into the engineer's outfit, hoping that the other members won't notice the spatters of blood on the red of the uniform.
There is still one last sentry left between your team and the intelligence that's your employers paid so much to have. You slink your way through the base, avoiding eye-contact with your enemies. At last, you see it, the last sentry. It's a monstrous thing, looking as big as the engineer that's guarding it.
This one seems more wary of the people around him, keeping his shotgun in his hand at all times. It doesn't look like you'll be able to approach him without getting shot. You do the next best thing. You hide just out of the view of the sentry and take out your handgun. There's a bit of a distance, but it's still child's play to you. You place a single bullet in his head and quickly hide around the corner.
You have to act fast now. No doubt his teammates would have heard the shot, and were rushing here right now. You slap an electro-sapper onto the sentry and scream at your team to go. As you turn to escape, you see him, and he's grinning. You look down, and to your horror, you spot a pipe bomb right at your feet.
As you turn to run, they explode. A corpse hits the floor, and the demoman throws a taunt at your dead body... well, it is suppose to be you anyway. You're low on health, one of your legs are almost completely gone. Thankfully, his attack activated your dead-ringer, which had the secondary effect of dropping your supposed corpse onto the floor. You quickly don your disguise and limp right out their front door.
Your job is done... for now.