Unlike Father, Unlike Son

In the cells of the Saint Marie court house, murder suspect Jack Harmer, awaiting trial, is shot dead by a killer that would have had to pass through three locked doors and past Dwayne and JP. Humphrey eliminates suspects to an initial three and then four, but cannot deduce how the murder was committed and what happened to the murder weapon, until he remembers ants coming through a window into the cell, leading to the solving of two murders. Humphrey's father comes to the island to convince him to come back home to Britain for his ex-wife, Sally, but watching his son solve the case realises he is happy for him to remain in Saint Marie.