Thunderbirds (TV series)/Recap/S1/E17 The Man From MI 5

Aboard his luxury yacht in the harbour of Monaco, a British agent in possession of secret papers is brutally gunned down. The papers are stolen and the yacht is mined, taking it to the bottom. While the British Security Service quickly determines that this was murder and not an accident, they are unable to progress the investigation. The leader of the investigation calls in an old friend - Lady Penelope Creighton-Ward.

While Lady Penelope quickly identifies those responsible, she's hampered in her investigation after they tie her to a chair and place a timed explosive by her feet. The explosion should draw off the investigators and allow the criminals to escape in their submarine. Unfortunately for them, the crooks hadn't counted on the fact that everything Lady Penelope owns has a radio in it, and International Resuce arrive rapidly to save their friend. Thunderbird 1 brings Scott to save Lady Penelope from the bomb, while Thunderbird 4 pumps the submarine full of knockout gas.