This book relates a love story between an American Professor of history, Chris, and an English lady, Valerie he meets while she is on vacation in Paris. She is an aspiring painter working in a London book store to make ends meet. They are both nearing forty and decide to do a trip to Burgundy where Chris wants to study the local wines for a book he plans to write. After that Chris begins to teach American history at the Institut d'Anglais for French students studying English. There he meets a French lady, Claudia, who he likes very much. Valerie becomes jealous of that and Chris with the numerous flirtations Valerie likes to do, which explains the title, "Paris Triangle.". Chris also becomes friends with a pilot of Air France, Francois, and they fly around Paris together in his small plane. . There are stories about the adventures and love affairs of Francois.
Chris and Valerie make a small trip to Belgium for the Christmas holiday and a longer one to Rome for the Easter holidays. Towards the end of the book Chris does a bike trip through southwestern France with Claudia and her new boy friend, Guy.
Returning from that trip, Chris decides he only wants to be with Valerie and talks her into returning to New York with him where he will resume his teaching job at Baruch College. The book ends with their boarding the Air France flight to New York.