Robert B. Parker's Fool's Paradise

When an unknown man is found murdered in Paradise, Jesse Stone will have his hands full finding out who he was--and what he was seeking. When a body is discovered at the lake in Paradise, Police Chief Jesse Stone is surprised to find he recognizes the murder victim--the man had been at the same AA meeting as Jesse the evening before. But otherwise, Jesse has no clue as to the man's identity. He isn't a local, nor does he have ID on him, nor does any neighboring state have a reported missing person matching his description.
Their single lead is from a taxi company that recalls dropping off the mysterious stranger outside the gate at the mansion of one of the wealthiest families in town.