We have been to Paris before but are flying from Dublin, Ireland to Paris then renting a car and driving to Normandy. We are taking our Grandson (18) with us on this trip and he wanted to spend a day in Paris after seeing Normandy. We will leave France from Paris Gare Du Nord to London. What is the best way to make this happen. We will be in Normandy are two or three nights and this trip will be in late June 2017
I may be missing something, but "making this happen " looks awfully simple to me. If your grandson wants you all to spend a day in Paris after Normandy, what exactly is the problem?
You drive to Paris and drop the car at the airport or at a rental agency in town then you spend a day in Paris and take the train the next day.
If the grandson want a day in Paris, you will have to plan 2 nights there, or else take a very late train to London. Otherwise it's really only half a day. It won't be very satisfying.
You can take a train to Paris from many destinations in Normandy and Brittany if that helps. If so you can usually return the car near the train station.
I'd return the car in Caen and take a train into Paris. What time does your train leave for London?
Since the trip is planned for June of 2017, I doubt any concrete arrangements have been made, i.e., plane and train bookings, which makes it even easier to fit in a day in Paris. However, until the OP returns, we can't really offer useful advice.