'Dragonsfield' by Terence Feely

After a scientist is badly exposed to radiation, Steed is sent to investigate a spacecraft facility that is working on making a special material to shield astronauts from radiation. Working alone, Steed discovers that the security officer, Saunders, has warned Doctor Alford, one of the team of scientists, about fraternising with his assistant Susan Summers. After rescuing Alford from an unknown assailant, Steed is almost killed when someone tampers with the equipment that he has volunteered to test. He then learns that Saunders has cracked the saboteurs’ code, and has arranged a meeting at the local pub; but Steed arrives too late, and finds that Saunders has been captured by two gunmen. Steed tracks them down to a disused flour mill, rescues Saunders, and forces one of the gunmen to reveal the identity of the saboteur: Susan Summers. Steed rushes back to the research centre, just in time to stop Susan from killing another member of the team.

Ian Hendry (Doctor David Keel), Patrick Macnee (John Steed), Sylvia Langova (Lisa Strauss), Alfred Burke (Saunders), Ronald Leigh-Hunt (Redington), Barbara Shelley (Susan Summers), Thomas Kyffin (Jack Alford), Keith Barron (Technician), Amanda Reeves (Secretary), Eric Dodson (One-Fifteen), Steven Scott (Boris), Michael Robbins (Landlord), Herbert Nelson (Peters), Morris Perry (Second Technician)

Directed by Peter Hammond
Produced by Leonard White

TX:
UK: 30th December, 1961

Notes:
*Featuring John Steed

*Original title: ‘The Un-Dead’

*This episode no longer exists