The best way to describe "Common Foe" is with this:
Your vacation has been cancelled.
That is what Jean-Val Fincoeur finds out when he and his Canadian friends come across some information while attending the celebrations of the supposed crash of a UFO near Roswell, New Mexico. The information sends Jean-Val on a daredevil run for the Canadian border with the most powerful intelligence agency in the world doing everything they can to prevent him from getting home with the evidence he is carrying.
Being in business is a gamble, but gambling with your life is a dangerous business. Ex-American and new Canadian citizen, Patrice Fincham, learns that lesson the hard way when she begins investigating the history of a bank account owned by a Royal Canadian Air Force pilot that died more than fifty years ago. Canada's Intelligence agency, CSIS, will do whatever it takes to prevent Patrice from discovering how and where that pilot died.
Although they don't know it, Jean-Val and Patrice have come across two secrets that are so incredibly interwoven that it might be assumed they were working together.