Chance Assassin Series by Nicole Castle

Vincent Sullivan is down on his luck. When a chance encounter generates a job prospect he’s too desperate to decline, Vincent is well on his way to a career in crime. But after the job goes wrong and he’s gravely injured in the process, things couldn’t get much worse. Except that he may have just killed a man. With the entrance of a mysterious stranger, life is finally starting to look up. Unless his luck is about to run out for good.

Two years following the events of Chance Assassin, Frank and Vincent are living in France, struggling with retirement. And with each other. When someone from Frank's past shows up and threatens to bring his personal and professional lives together with a bang, it's up to them to find out who ordered the hit and take them out first. Things may not be what they seem, but they may be exactly what Frank and Vincent need.

With a new handler and Silva's book of hits, Frank and Vincent's marital bliss is only interrupted by the occasional spat over whose turn it is to kill. But when their jobs stop going according to plan, a detour takes them down a path that could bring the end of their careers. And their lives.