Valerie Mayberry is an agent with the FBI Counterintelligence unit.
Brett Garrett is a former U.S. Navy SEAL.
When we first meet Mayberry, she is well into her normal six-mile morning run, done to lift her moods. Mayberry is need of them every day because she routinely "awoke sad", missing her late husband Noah, killed in the line of duty. This source of grief is especially difficult for her because of her phenomenal photographic memory that would not let her forget anything, even those things she really needed to let go.
Mayberry works for the FBI because of two reasons; she enjoys it a lot and she is good at doing it. She did not need to work due to a trust fund that provided nicely for her but needing something to occupy her highly intelligent mind, especially now that she no longer had Noah, work provided a much welcome distraction as well as a vocation.
Brett Garrett is, on our first meeting, working for a private contractor providing security for VIPs. This current assignment has he working protection detail for a US ambassador in Ukraine.
A flashback scene early on lets us follow the events that will drastically change his life and put him in the position he will be when he starts work with Mayberry. It was two years before. Garrett had been a SEAL Chief Petty Officer having served in the Navy for the previous 14 years. Now 34 years old, he was in charge of a mission in Cameroon where his team had taken on a squad of Boko Haram fighters. 19 of the 20 terrorist had been dispatched. The 20th was taken out by Garrett's rifle shot from inside the helicopter lifting his team to safety but not before that man released an RPG. Everyone in the chopper were killed except Garrett. Unfortunately Garrett had been operating against orders to try to save a group of children. And one of those in the team who died was the son of an influential Senator.
Now back in the present, even though he is more than qualified to do his job, his notoriety from that failed rescue mission made him toxic whenever anyone recognized him, which a lot of people did a lot because the Senator was extremely vindictive.
The two will be thrown together and will find that they compliment each other nicely, which is good because there will be a lot of bad people trying very hard to kill them both.