Deaf botanist Alan Carter's fiancee walks away from their floral bliss under some strange influence, and is picked up by an entranced chauffeur. Has it got anything to do with the giant seed from outer space that has landed nearby?...

Trusted agent Melville has lost three partners in quick succession, and seems to be lying at every opportunity. Is he really the man to partner Steed in an attempt to convict Lord Edgefield, noted blackmailer? And what is the odd connection between this whole affair and daily milk deliveries?