'Dangerous Cargo' by Dennis Spooner

Steve, Venus and Matt take Fireball Junior down to the surface of Pharos, a world that was once the site of a busy ciluvium mining operation, but which is now crumbling into dust and decay. After Steve recommends to Commander Zero that the unstable planet be demolished, he is ordered to return to Pharos with Vesuvium Nine, the most powerful explosive known to man. The crew are unsettled by the presence of such a dangerous substance on board; then things get worse: when they return to the planet, Steve and his friends find themselves trapped in a mineshaft by their enemies, the Subterrains…

Paul Maxwell (Colonel Steve Zodiac), Sylvia Anderson (Doctor Venus), David Graham (Professor Matt Matic / Lieutenant 90 / Zoony the Lazoon / Subterrain 1), John Bluthal (Commander Zero / Jock Campbell / Subterrain 2), Gerry Anderson (Robert the Robot)

Directed by Johnn Kelly
Produced by Gerry Anderson
Associate Producer Reg Hill

TX (UK - ITV):
19th August 1963

Notes:
*Featuring Colonel Steve Zodiac, Venus, Professor Matt Matic, Commander Zero, Lieutenant 90 and Robert the Robot