A writer is down for the murder of his wife and her lover, but she's left a contradictory note. ""Who builds stronger than a mason, a shipwright, or a carpenter?""

Cannon begins to see a doubtful situation. ""The houses he makes last till doomsday.""

Cannon and Barnaby Jones investigate the death of a young woman who was about to expose the illegal activities of the large corporation she was working for.

The crossover continues on Barnaby Jones S04E01 The Deadly Conspiracy (II).