Bitter Night. The McLaren Mysteries, #20

When former police detective Michael McLaren is given an old photograph and newspaper article, an inquiry begins that seems straight forward enough: an accident in a millpond. But when it's apparent that other odd deaths are linked to this, all via the victims receiving a cypher puzzle, the secret meanings become more important. More important still when a fifth death occurs practically on McLaren's doorstep.
Now it's five deaths and five puzzles, and McLaren's determined to solve the mysteries. The only problem is that the trail he's following entraps not only himself but also his friend, Jamie-traps that might be impossible to escape.