Steed attends the funeral of a former colleague and not only suspects foul play but is struck by the fact that the tiny, isolated Cornish churchyard contains the corpses of several worthies hardly to be associated with the area. His investigations lead to a sinister assassination bureau, Mandrake Investments, who bury poison victims in the churchyard because its proximity to an old tin mine means that the nature of the soil prevents the detection of the poison.

Also on The Avengers: Season 3, disk 6

An agent is killed at a wine shop and Steed realises that one of two brothers, Frederick Paignton, who work in the shop has been blackmailed by his boss into the murder. In the shop's cellar there is a dark room, 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.

Also on The Avengers: Season 3, disk 4

Whilst protecting the race horse of a visiting dignitary in England for the current racing season Steed observes that George Meadows, owner of the livery stables, is behaving oddly. This leads him to uncover a murder organization in which jockeys with high-powered binoculars single out chosen victims and kill them with poison darts.

Also on The Avengers: Season 3, disk 6