Hollis and Finn Larsson are college professors.
They are a married couple who are both instructors at Bradford University, "a small but prestigious institution in Southwestern Michigan". Both have recently turned 40 years old and both have keep in reasonably good shape, Hollis more than her husband, Finn, since she is active in "running, yoga, boxing" and whatever else she can work in. Finn is a bit more sedentary when we meet them initially, having become a recent die-hard fan of baseball and is glued to television for any Cubs game. A couple years before, it had been archery which at least got him outdoors on occasion.
Finn is a "nationally recognized expert in European literature", accordint to Hollis though Finn quickly amends that to be "internationally". Hollis teaches courses in both History and in World Politics, the latter being her key interest though during the time we follow their adventures, she has been planning and then writing a history of the United Nations. Since both have achieved tenure at that institution, both have achieved their initial goal in life and have reached a good level of security.
It is Hollis that is feeling a bit of unease in her life - okay, she has gotten more than a little bored. She loves her husband and loves teaching and truly enjoys Bradford. There is just something missing, a sense of adventure to give her some drive back in her day-to-day. Not so much with Finn, at least not at first, as there was always it seemed another baseball game coming up and for a real exciting time, how about a trip to Chicago to take in a Cubs game live.
That is when Interpol comes calling. Not the whole organization, of course, but one individual. David Agnelli, an old friend from before she met Finn; "so old time she'd never mentioned to him" which presented "a whole can of worms she'd hoped never to open". And with his visit we learn how Hollis had thought for a time of joining the CIA and had even graduated the Agency's Farm training at the top of her class before deciding on returning to Michigan. Agnelli had been in that same class and had gone on to work for the CIA for a time before making a switch to the State Department and through it, Interpol and a little known department in that organization.
Which is how the Larssons will find themselves involved in far away from their comfort zones.