Good stuff
Ok, before I start please keep in mind that it could be just me being picky here so don't take it too much to heart.
The first thing I noticed was the amazing amount of short sentences. Shorter sentences and even fragmented sentences can be used and are usually used for effect. I understand your story needs this as it is not a ponies in the flowery field type text, but I think you might have gone a little overboard on the short sentences. It probably needs to be less choppy.
"I lean back against the wall, however jerk back forwards as the horrible grimy lime scale strokes my neck."
I don’t think the "however" is right for this phrase and the "jerk back forwards" takes time to process because it's almost an oxymoron. Maybe try " I lean back against the wall, yet jerk back upright as the horrible grimy lime scale strokes my neck."
"I feel my Adams apple leap down my throat"
For this, I can see where you are going but I don’t think that “leaping” and “down” work together.
"opens my hand and places the knife inside it."
I don’t think it is a specific knife yet just because you haven’t mentioned it before. Try "a knife."
"They had vanished. The carriage shook. The carriage went dark. The carriage went silent." Although I mentioned the many short sentences, I like the use of that here.
I really like what you’ve done here over all and there is not much to say about it.
Your use of the sense of smell at the beginning was very convincing and adds to just the use of sight as a describing tool.
The ending was excellent.