Borrowed Trouble is not the typical sequel. The first book, One Too Many Blows to the Head was a gem. I don't know anything about boxing or people connected with that occupation, but that didn't interfere in any way with my enjoyment of One Too Many... The characters are rich and real and everything was explained very clearly while still maintaining the atmosphere of a story. It never came across like reference material about fighting. All you did when you finished reading that one was anxiously await the sequel.
Most sequels are extremely boring and simply try to cash in on the success of the original. It is rare that a sequel can stand on its own merit. Borrowed Trouble is the exception. While it does help you to understand the primary characters and their relationship to each other to have read the first book, it is not necessary. There's sufficient backstory in Borrowed Trouble to enable that story to stand on its own. There isn't too much however, and Borrowed Trouble never lingers too long in the past or drags you into the prior story. It's just enough to familiarize you with the unlikely pairing of these two characters.
I enjoyed Borrowed Trouble very much. I've read other books that had more than one author and there are generally points where you can see where one left off and the other began. Not so with One Too Many Blows... or Borrowed Trouble. The story flows flawlessly throughout both books, and never misses a beat. The characters stay vivid throughout both books and I have to say, I don't know if there are currently any plans to continue to another book, but I would certainly hope there is. All I wanted to do when I finished Borrowed Trouble was to pick up the next. I will anxiously await another sequel and I sincerely hope these authors will provide one.