- "My, this is a deserted area. One just wouldn't know where one was, would one?"
— "Gayle Williams"
The British government asks for International Rescue's help in locating the missing blueprints for an atomic weapon. Whilst tracking the culprits, IR agent Lady Penelope (posing as model Gayle Williams) is kidnapped and held aboard a bomb-rigged boat. Scott and Gordon have very little time to locate and rescue her, and steal back the plans...before the bomb explodes, and the villains escape...
- Main article: The Man From MI.5/Storyline
- Main article: The Man From MI.5/Transcript
- Jeff Tracy - Peter Dyneley
- Scott Tracy - Shane Rimmer
- Lady Penelope Creighton-Ward - Sylvia Anderson
- Virgil Tracy - David Holliday
- Alan Tracy - Matt Zimmerman
- Brains - David Graham
- Parker - David Graham
- Tin-Tin Kyrano - Christine Finn
- Gordon Tracy - David Graham
- John Tracy - Ray Barrett
- Jimmy Bondson - Ray Barrett
- Carl - David Graham
- Ritter - Ray Barrett
- The Third Man - Matt Zimmerman
- MI.5 Agent Tidman - David Graham
- Fireflash Stewardess (off screen voice only) - Christine Finn
International Rescue Equipment UsedEdit
- Thunderbird 1
- Thunderbird 2 (Pod 4, containing Thunderbird 4)
- Thunderbird 4 (Harpoon drill, with knock-out gas)
- Thunderbird 5
- FAB 1
- FAB 2
Non-International Rescue Equipment UsedEdit
- First Appearance: Lady Penelope's yacht, FAB 2. (It will later make an appearance in Introducing Thunderbirds, for Thunderbirds 1965.)
- The model submarine Brains used for his experiment in the Tracy Villa pool was also used as The Hood's 3E Submarine in Desperate Intruder. (It even still has 3E written on the sides!)
- This episode features the first full Thunderbird 4 launch sequence, shown from inside Pod 4. (Prior to this, TB4 had only been seen emerging down the ramp outside the pod door.)
- It's also the only occasion wherein Thunderbird 2 gently rests Pod 4 upon the surface of the water (rather than dropping it in), and then rises clear with its lifting jets.
- The backdrop used for the harbour scenes also appears in the opening scene of The Duchess Assignment, in the Captain Scarlet and the Mysterons episode Model Spy, and in the Joe 90 episode The Race.
- When broadcast in the half-hour "cliffhanger" format, Part One concluded with Carl taking off in his boat, with Penelope as his prisoner, from FAB 2.
- Main article: The Man From MI.5/Goofs
- French: L'homme du M I5
- German: Der Mann vom M.I.5
- Spanish: El Hombre del MI.5; El agente MI5 (DVD)
- Italian: S.O.S. Servizi Segreti Britannici
- Dutch: De geheime agent (TV); De man van MI. 5 (VHS, DVD)
- Japanese: 情報員MI. 5