Warnings: Graphic description of injury. Also, I probably should've said this at Chapter 1, but if you're seriously claustrophobic, you might not enjoy certain parts of the fic very much (particularly some of the later chapters, this one isn't that bad). Then again, the story does take place in a cave, so that's probably not a huge surprise to anyone.

The cave entrance really was narrow, almost too narrow for Steve to operate his descender in it, both his back and chest rubbing against rock. At least the walls were smooth, with no risk of anything snagging.

He couldn't help thinking about how difficult it would be to bring someone who was injured through this thing.

Thank goodness, the narrow part went on only for maybe a dozen feet, and then it widened into a more spacious ravine, a deep, narrow canyon. The rope was hanging freely in the middle of it. The walls behind and in front of him were still close enough that he could easily touch them if he reached out, but to each side, he couldn't see where canyon ended. He looked up, and could only just see the daylight he'd left behind.

Soon, he spotted Bruce and Natasha's lights below him, and heard their voices. The sound echoed so much in the high narrow space that he couldn't make out the words.

At the end of the rope, he landed on a rocky floor, and took in his surroundings. It seemed they weren't actually at the bottom of the canyon, but walking on some very large boulders that filled it completely. Bruce and Natasha were standing on the edge of one them, staring ahead, along the long axis of the canyon. Bruce had his map-tablet out.

"We should keep following this passage for as long as we can," Bruce said. "It's the easiest way to the lower levels of the system."

"Do you think – are these boulders stable?" Steve asked, remembering full well the collapse they'd witnessed earlier.

"Technically, you can never really be sure," Bruce replied, not too reassuringly. "But I'd not worry about it too much, they do look like they've been wedged here for quite a while. I think we can climb down without expending any rope," he motioned at the direction where he and Natasha had been looking. The way on was a series of boulders forming a slope with occasional steeper drops.

"I should probably go first," Steve suggested.

Bruce gave him a disappointed look. "If you're worried I'll suddenly lose my temper, you should have left me on the surface. Remind me again, how many limestone caves have you visited?"

Well, Steve had been to Mammoth Cave once, when it was a brand new attraction, on a promotional tour. He didn't say that aloud. And he did have his doubts – the combination of an unfamiliar, challenging environment and the knowledge of how difficult the Hulk was to control made it hard not to be a little concerned. He didn't say that either.

What he did say was, "It's not that. But if there's some kind of a landslide, I've probably got the best chances of surviving it."

"As long as I'm here, I'll go first. I'll know where to step, there won't be any landslides," Bruce declared.

"You boys done yet? We should get moving," Natasha said. "And for the record, if we hit anything really tight, I'll be the one to go first."

Tony had finally finished the excruciating process of cleaning the injury. Time for the moment of truth. Terribly anxious, he forced himself to look at his leg again, to really look at it properly, which he actually hadn't done yet.

He was underwhelmed, truth be told.

Not that it wasn't bad, it definitely was. Just the fact that the suit's plates were broken and twisted enough to reveal glimpses of his undersuit and skin made that quite clear. But now that he'd washed off the worst of the mud and gore, there didn't seem to be quite as much blood as he'd first thought, and the fracture was only bleeding sluggishly. Some of the blood was coming from where the sharp metal edges of broken armor had cut into his leg, which definitely wasn't nice at all, but those wounds were mostly superficial.

The worst of it, the exposed segment of tibia, less than two inches of it, wasn't really sticking out very much, it was just there, in the middle of the torn skin and undersuit and suit. Seemed like a clean enough break, too, no additional bone fragments as far as he could see. Yeah, not at all spectacular then. Perfectly fine. He'd just hop up and walk out, no problem. Not.

He realized he was chuckling, just a little bit, just slightly hysterical and breathless. It was really starting to hurt his ribs, but they were nothing compared to his leg, so he could easily ignore them.

"What is it, sir?" Jarvis asked, sounding uncertain.

"I just, you know, it's actually not that bad. It's probably the single worst fracture I've suffered in my entire life, and still, it's not as bad as I thought. I had no idea you could stare at a visible bit of broken bone in your leg and think that it's not that bad," Tony babbled.

"I'm not quite sure I agree with your assessment. You are correct that the break does not appear immediately life-threatening, but the risk of severe complications remains, and you are in urgent need of medical attention."

"Tell me about it. Now, I guess I'd better bind it up."

He obviously didn't have any bandages with him, so it was a practical challenge to figure out what to use. He ended up taking the armor off his good leg so he could cut the undersuit into suitable strips. He took his time doing that, and rebuilding the armor around his leg. After it was done, he carefully wrapped the sliced neoprene around the injury. That, of course, also hurt like the dickens, but finally, after a lot of swearing, moaning and whimpering, it was all done.

His head swimming, he cautiously lay down on the ground again. "Remind me to design some kind of an IV painkiller system into the suit the next time I make upgrades."

"Duly noted, sir."

Although the canyon was so high that they couldn't see the ceiling, it remained so narrow that they had to advance in single file. They kept clambering downwards, one boulder after another. It wasn't very difficult, but some of the climbs were tricky, since they required balancing on very small and extremely slippery holds. Many times, it would have been faster to leap down, but Steve was not keen to test whether the boulders would hold if he did.

They didn't encounter any major difficulties, and they didn't need to use any rope. They all were well suited for this, Steve with his enhanced physique, Natasha with her agility and training, and Bruce with his careful concentration and experience of underground spaces.

They kept moving downwards for what felt like at least two hundred feet. That was great, because it meant they were constantly getting closer to where they were hoping to find Tony.

Steve tried not to think too much about it, but he wasn't sure how realistic it was to expect that they might actually find him. His imagination kept conjuring up all sorts of worst-case scenarios, visions of massive piles of boulders with a gold-red gauntlet or a bloodied hand reaching out from under them. They didn't even know for sure that Tony would be at the bottom of the collapse – really, what reason did they have to expect that he would be? Maybe he was buried somewhere in the middle of it, unreachable. Maybe he was already dead. But they had to do something, and this was their best shot.

He surfaced from his gloomy thoughts when they came to face the biggest drop yet.

"Around fifty feet, by the looks of it," Natasha said from where she was standing, just behind Bruce, who was kneeling at the edge, looking down.

"It might be possible to free climb this," Bruce noted. "But I think we'd better put a rope on it. There are bolts here as well, we've got plenty of rope, and it will definitely make this a lot easier coming up."

Especially if we're coming up with someone who's injured, Steve added in his mind. That was the other thought that he just couldn't shake. So far, everything they had done had been easy enough for three people who were in good shape, but for anyone who wasn't – let alone carrying someone...

Steve pulled out a stretch of rope from his pack, and handed it to Bruce, who attached it expertly, and rappelled with practiced ease.

The bottom of the rope finally brought them to the bottom of the canyon: the floor was mostly compacted mud and some rocks here and there. The passage was also more spacious than anything they'd seen so far, wide enough for two people to walk abreast.

Steve checked the time. Thirty-five minutes since they'd come in, and they had already covered most of the vertical distance. They were making good time. On the other hand, put that together with the time it had taken them to prepare, and it meant that Tony had already been missing for over an hour.

Bruce was looking at the map again. "This passage goes on for almost a mile, but it's not quite in the right direction. We should start looking for one that leads to the right instead. There are several potential routes that I can see, but I'm not sure if all of them are feasible. We'll just have to find out by trial and error."