A secretive, lonely hitman is asked to perform one last hit when he decides to quit after falling in love with a successful attorney. When the target turns out to be his intended, he must bring all of his skills to bear against everything the mob can throw at him.

Falling in love is the strongest motivation for retiring and the strongest motivation for wanting to risk all to save her life.

Best to decide whether falling in love is the inciting incident in which case this is a love story set in a crime world. Or been given his lover as a target in which case this is a crime or crime/thriller.

Accordingly the inciting incident of choice needs to be put forward and as the others have mentioned already cut the first sentence as it is mostly back story and unrelated to the plot at hand.

Hope this helps.

After falling in love with a brilliant attorney, a hit man vows to retire but the mob boss won't let him until he performs one more job: murder the attorney. Now he must fight to save her life -- and his. (40 words).

Although the obvious implication is that his own life is in jeopardy so maybe "-- and his" is superfluous and can be dropped which reduces the word count to 38.