Yes I'm also stuck on stage 4.
This hunt started out with some fairly straight forward puzzles which have progressively become more difficult as each stage is solved. Stage 4 (the final solution) is by far the most difficult with very little clues or anything to really go on. I think Murray Bailey always planned this to be the "real" hunt. Everything so far has been quite fun and I must say that I'm really enjoying it, but stage 4 is proving to be a bit frustrating. I've tried many approaches over the last few weeks but haven't even made a dent in it... I'm beginning to run out of ideas.