My wife and I will be traveling from Paris to London and were debating flying vs. the Eurostar. I think I've settled on Eurostar due to its added convenience. I went to www.eurostar.com and saw that we can "non-flexible" fares for US$89. "Semi-flexible" fares jump up to $168. I read the descriptions of each, but can't really tell any difference. Can someone guide me here? It's a huge price difference, but I'm concerned that there is some catch with the non-flex fares that I will find out about at the train station and wish I had paid more for the semi-flex fare. Anyone know what these are and have a recommendation?