Die Dreaming (Owen Keane Mysteries) (1994)

Ex-seminarian turned seeker of lost souls (and bartender) Owen Keane attends his tenth high school reunion and finds himself the butt of a practical joke by the old gang. (Instigated by his posting himself as running a detective agency). Vengeance being the operative mood in his "morning after" state, he starts asking sticky questions about a decade-old secret regarding a member of the class who didn't attend the reunion, an ex-addict Vietnam vet, Ricky. What he discovers is shocking, but pieces are missing. Not until the 20th reunion do they fit together. Ricky has been murdered and Owen is determined to unravel the tangle of lies that cost a man his life, and now may cost Owen his own.