Sadly, my library only has back to Spencer book #16 "Playmates" so I will try that.Robert B. Parker: The Spenser books were the basis for the "Spenser: For Hire" TV series with Robert Urich from the mid-80s. Spenser is a smart-alack ex-cop turned PI. Some of his wise cracks are quite funny. While the plots are all very serious, Spenser's attitude about things keeps it a bit lighter. "The Godwulf Manuscript" is the first in the series and is as good a place to start as any.
There are two long term story arcs in the Spenser books I've read so far -- his relationship with his girlfriend Susan and a quasi-parental relationship with a younger man named Paul that he helped extricate from a very bad situation. Neither of these are such that you'd be lost picking it up in the middle. The other recurring characters are more don't have as much critical backstory associated with them.Sadly, my library only has back to Spencer book #16 "Playmates" so I will try that.