An agent is killed at a wine shop and Steed realises that one of two brothers ,Frederick Paignton, who works in the shop, has been blackmailed by his boss into the murder. In the shop's cellar there is a darkroom, used to develop military secrets on microfilm. Frederick's brother Allan's fiancee Marion, meanwhile, is being forced to shut down the security system at the research station where she works. Mrs Gale investigates the latter - whilst Steed employs his nose for a good vintage.
—don @ minifie-1