I thought I had done this, but the end game has me perplexed. I am deeply confused by 31a, as I have a possible answer that fits the journey, but I cannot parse it at all. Then, as for the end game - If my 31a is right, I have 5 points on the round trip, or 4 points for the outward journey. If the preamble asked to replace one symbol with the other, or to superimpose two symbols, I would have a solution for the round trip, but it specifically states to replace a letter - which one, I haven't a clue. Playfairs always scare me, but the 2 obvious places on the journey made identifying the code word(s) quite straightforward. I shall remain baffled. My solution for 31a is 8 letters long - is that correct?