USA-London-Paris-USA

Hi Lynn. I did this trip in reverse a few months ago: STL to Paris, Eurostar to London, and London to STL. Do you have only 6 days for sightseeing? You'll lose half a day in transit between London and Paris, just FYI. Book Eurostar tickets on eurostar.com. You can book as far as 120 days out, and the tickets are cheaper the father in advance you book. You'll have to buy plane tickets on a different website.

That means I have to purchase one-way plane tickets then, correct?

You have to book the air and rail separately; the good news is, you get the best prices by doing this. Do NOT book two one way air tickets; this costs much more than "open jaw" (called "multi city" on booking sites). To book your air: 1. Look at Kayak or Matrix ITA. 2. Choose "multi-city" rather than "one way" or "round trip" 3. For you first leg, put in Akron to London, and for your second leg, put in Paris to Akron. When asked to choose London airports, choose LON (all London airports) and for Paris, choose PAR (all Paris airports). For Akron, be sure to check "include nearby airports" to pull up Cleveland as well (or just enter CLE, CAK to get these two).
4. See what comes up. 5. If what comes up is not satisfactory, or if you have other questions, post the details here. To book your train between London and Paris, follow the advice above, and book at Eurostar.com as close to 120 days before your travel as you can. Eurostar fares go up the closer to your travel date and as trains fill up, and like airfares, the cheapest fares are non-refundable and non-changeable, so don't book until your are sure of your plans (or pay more for a changeable ticket). Got to the website now to familiarize yourself with the options, so you'll be ready to book quickly when the 120 day window opens. Someone will surely tell you to spend all of your limited time in one city or the other. If that's what you want to do, fine; but if you really want a taste of both cities, don't let anyone tell you it can't be done. Just accept that you will be getting only a taste.

I have done this exact trip twice, in both directions. I spent about the same time in each city as you are planning to do. If you prioritize your time and pick and choose what you want to see, then you can get the flavor of both cities in three days. I agree, don't let some of the other posters talk you out of what you want to do.

Sure. As another suggested, check out Kayak and hit "multi-city". Just to give you an idea of how fare differences can be, I searched a random set of days in June for you. CAK-LHR/CDG-CLE: $1341 (not including any travel inside of Europe. You need LHR-CDG by train or plane) CAK-LHR/LHR-CAK: $1234 (also not including any travel inside Europe.)
CAK-CDG/CDG-CAK: $1315 (also not including any travel inside Europe.)

It is too bad you only have three days in each city. We have been to London four years in a row. We have spent about six weeks there, total. We also went to Paris two years in a row, for a totatl of a month. We still want to go back to both cities. They are so beautiful and there is so much to see inside/outside of both London and Paris.

We always fly into Heathrow, spend half our time in London, then on to Paris via Eurostar. We return to London the night before our early flight home to the US and stay at Jury's Inn close to Heathrow. It's only 2.5 hours from London to Paris via Eurostar so you can have plenty of time to sample both cities. Works like a charm every year.