'Death on the Slipway' by James Mitchell

Steed poses as a metallurgist in order to enter the dockyard where a nuclear submarine is being built. Here he encounters an old nemesis, Kolchek, who blackmails the yard foreman into planting a bomb to kill Steed, so that he can obtain the plans to the craft. When Steed catches Liz Fleming, the foreman's lover, searching his room, he is able to learn about the bomb. He manages to find it, throwing it into the water just before it explodes.

Ian Hendry (Doctor David Keel), Patrick Macnee (John Steed), Peter Arne (Kolchek), Frank Thornton (Sir William Bonner), Nyree Dawn Porter (Liz Wells), Paul Dawkins (Sam Pearson), Sean Sullivan (Fleming), Redmond Bailey (Geordie Wilson), Robert G. Bahey (Jack), Barry Keegan (Inspector Georgeson), Tom Adams (P.C. Butterworth), Douglas Muir (One-Ten), Gary Watson (Pardoe), Patrick Connor (P.C. Geary), Hamilton Dyce (Sergeant Brodie), Billy Milton (Chandler)

Directed by Peter Hammond
Produced by Leonard White

TX:
UK: 24th June, 1961

Notes:
*Featuring Doctor David Keel and John Steed

*Nyree Dawn Porter, who plays Liz Wells, was the producers' first pick to play Cathy Gale in season 2

*This episode no longer exists