Murder on the Rhône. Captain Lacey Regency Mysteries, #18

In June, 1820, I travel to Lyon to attend a wedding, looking forward to sunny strolls on the city's two rivers and sampling the region's food. Instead, I soon spy a man from my past who stirs painful and enraging memories. I find the same man bent over a corpse on one of the city's bridges one morning, holding a blood-soaked knife, but he insists he is innocent of the murder. I'd like him to be responsible, but my experience investigating problems of this sort tells me he is not.
Suspicion, unfortunately, falls on the family my daughter is about to marry into, whose high standing and respect from the townspeople will not help them against the gendarmes determined to solve the crime. When I look into the matter, I dredge up dark things from that family's past that they will do anything to keep me from discovering .