The Avengers.S06E15.The Rotters

Steed investigates a firm named WormDoom, whose proprietor, a businessman widely thought a bit of a rotter, is killing off his business competitors, all experts on timber decay. To get at his victims, he has stolen a new chemical that, while simulating dry rot, causes wood to rot instantaneously: turning doors, walls and windows all to powder.
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Teleplay by Dave Freeman
Directed by Robert Fuest
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Guest Starring: Gerald Sim, Jerome Willis, Eric Barker, John Nettleton, Frank Middlemass, Harold Innocent, Amy Dalby, John Stone, Charles Morgan, Noel Davis