"Am approaching danger zone now. ETA four point five minutes."

Almost immediately, Alan's voice comes in response. "FAB, Virgil; the rescuees are on a ledge about eighty feet below the rim of the canyon at grid reference TL 27 Orange."

As I sit in the control room of Thunderbird Five, listening to the exchange between my brothers, I feel my fingers twitch towards the 'transmit' button', but I fight back the impulse. Alan sounds calm and in control of the situation; the last thing he wants is me sticking my oar in.

I keep a tight rein on my frustration as I recollect John's words the first time I did a stint on Five. "You have to remember, Scott, our role up here is to watch, gather and provide information, not to try and run things. If the situation changes, you pass on updates to the danger zone, but it's up to whoever is Field Commander to make the decisions."

I didn't really need the reminder. I'd been in the military long enough to know that you can't have two commanders on an operation - that way leads to chaos. It doesn't mean I have to like it though. I'm a man of action by nature, not an observer. I feel trapped up here in the sky. How do John and Alan cope? I want to be down there, at the sharp end of the action.

Under normal circumstances, I'd be pacing up and down like a bear in a cage by now, but I don't even have that option. I glance down, glaring at my knee in its heavy strapping. The fact that it's my own fault doesn't make me feel any better about it. I'd been out for my customary early morning run around the island last week when I tripped over a tree root and came crashing down, catching the side of my knee cap on a rock. I was about a mile from the house at the time. In hindsight I realise that I should have called someone to come and pick me up on a hover-bike, but though I considered the idea, I dismissed it. It was too early to think of getting Virgil out of bed unless I wanted him grumpy for the rest of the day, Gordon would have been doing his training in the pool and as Alan was due to leave for Thunderbird Five later that day, let's just say that I don't think he or Tin Tin would have appreciated being disturbed.

Besides, my knee didn't feel too bad at that point, so I decided to head back home under my own steam. However, by the time I had got back to the pool area I was beginning to regret my decision; the adrenaline rush had worn off and the joint was badly swollen and starting to throb. Gordon saw me limping towards him and rushed to my aid, helping me up to the house.

Brains examined me and declared that the knee was badly sprained, so it made sense for me to offer to relieve John on Five and let Alan pilot Thunderbird One. I can't say I was exactly happy about the idea, but I knew there was no way Father would let me go out on rescues until I had recovered, so I might as well make myself useful rather than sit around at home getting bored and frustrated.

"Am over rescue zone now; sending Gordon down with elevator cage." Virgil's voice over the speaker cuts into my musing.

I had picked up the call less than an hour ago from a party of seven hikers exploring the canyons of Arizona. They had camped for the night in the dry bed of the canyon but woke up when their camp-site started to run with water. Luckily, one of the group was experienced enough to realise the danger of the situation and get everyone onto a ledge partway up the canyon wall before the trickle became a tumult, sweeping everything ahead of it.

Alan's voice comes through the speaker grille again. "I'll drop One down into the canyon to give you a visual feed."

"Thanks, Alan. I'm having to stay above the rim; the canyon is too narrow at this point for me to get Two any lower."

What's that? Alan is taking my 'bird down into the confined width of a canyon in total darkness? That would be a tricky piece of flying for me to contemplate, let alone anyone else. My fists clench and my eyes are fixed on the read-outs from Thunderbird One's telemetry, but all the lights show green.

Another screen springs to life in front of me, picking up the images my 'bird is transmitting to her sister ship, and I see sheer rock walls catching the spotlight as the craft drops down. The image steadies as it picks out a small group huddled together on a ledge, uncomfortably close to the swirling dark waters below them.

The spotlight gleams off a metal box that descends from the top of the screen, dangling from the cable that connects it to Thunderbird Two.

I hear Gordon's chirpy voice, picked up by the microphone in the elevator cage. "Did anyone order a taxi? International Rescue at your service!" He always sounds cheerful and I'm sure his relaxed attitude must reassure our rescue victims. As I watch, the cage stops level with the ledge, which is now only a few feet above the turbulent waters.

A flash of blue from Gordon's uniform catches the light as he steps out of the cage. "OK, ladies and gentlemen, the cage will take four, so we're going to have to do this in two trips. Step this way, please, and mind the gap." A few moments later he calls out, "FAB, Virgil, take her away!"

The cage disappears upwards, out of the spotlight, and there is a few minutes pause before it descends again. But my attention is focussed on the figures on the ledge; one seems to be moving in an agitated manner, while Gordon's gestures seem to be attempting to pacify him. It's frustrating trying to work out what is going on; Alan must be feeling the same as I see him zooming the camera in, but at least here I can help. Quickly I open the channel to Gordon's watch, but set it to 'receive', and patch it through to Thunderbird One's cockpit to put Alan in the picture.

At once I hear raised voices.

"I tell you, I can't go in that thing, I just can't!" A man's voice has an edge of terror to it. "I only came on this trip because you promised there would be no climbing. I get vertigo! There's no way I can go up in that box!"

Gordon's tone is soothing, "Please try and stay calm, sir. I can strap you in once the cage arrives; you'll be quite safe."

A woman speaks next, her tone scathing. "Greg, don't be an idiot! You're going to have to do this. There isn't any other way!"

By now the cage is almost level with the ledge once more, and for a minute it obscures the figures. Then there is a shout, a scream from the woman, and I see a figure in blue tumble from the ledge.

"Gordon's in the water!" Alan's shout echoes my own cry of alarm.

My Field Commander training snaps into action, spurred on by big-brother instincts, and my mind races through the possibilities. Thunderbird Two has the elevator cage, but can it reach from above the rim of the canyon to water level? Thunderbird One can manoeuvre in the confined space but lacks a means of retrieving anyone from the water.

Alan must have been weighing up the same factors. I tend to think of him as impetuous, but that's just another name for quick-thinking, and now his voice has an edge of decisiveness I've never heard before. "Virgil, get the rest of that party off the ledge; I'm going after Gordon. Scott, I need you to track him for me!"

I jump when I hear my name and for a moment I freeze as my mind goes blank. I've only ever done this on the simulator before. A wave of relief washes over me as I recall the sequence to key in, then my fingers dance across the control panel, homing in on the signal from Gordon's watch.

Part of my mind registers Virgil ordering the rest of the group into the elevator cage; there doesn't seem to be any objection - I guess they must be too shocked to disobey. My attention is focussed on a small orange dot on my screen; at first it's moving erratically, and in my mind's eye I can imagine Gordon being tossed around by the current. But as I watch, the signal steadies and starts to move in a straight line.

Thunderbird One swings away from the cliff face and I see the camera play across the churning muddy waters. I don't know which brother I'm more worried about; Gordon at the mercy of the raging torrent, or Alan, flying a craft with an eighty-foot wingspan down a narrow canyon in pitch blackness, relying only on radar to avoid the rocky walls and any other obstacles that might be in his path.

As I watch, the orange dot comes to a rest.

"Hey, Alan," Gordon sounds slightly out of breath but still manages his customary laid-back drawl, "I've finished my swim practice for tonight; any chance of a lift home?"

As he speaks I let out the breath I hadn't realised I'd been holding, even as I patch his co-ordinates through to Alan. The camera zooms forwards until the spotlight picks out a rocky pinnacle sticking up out of the water; halfway up I can see a blue-clad arm, waving.

"Dropping a line to you now, Gordon." I can hear the tension in Alan's voice and can imagine his hands gripping the throttles as he inches his craft closer to the rocky peril that every instinct must be screaming at him to avoid. I realise my own fingers are clenched tightly on the arms of my chair in imitation of the same movement and make a conscious effort to relax them.

"I can see it! Down another ten feet. Five feet to the right. Got it!" I can hear movement then Gordon's voice again. "I've secured myself to the cable with my belt; haul away!"

Gordon isn't safe yet, and we all know it. Thunderbird One's winch is designed to lift objects, not people, and has no access to the cockpit. My heart is in my mouth as I watch my brother dangling, an unlikely fish on a line, as Alan lifts my 'bird out of the canyon, then moves the craft forward until it hovers over the rim. The picture steadies for a moment, then Gordon calls out, "FAB, Alan, I'm free now; take her away. I'll get Virgil to come and pick me up; that way I can get out of these wet clothes and ride home in comfort!"

"FAB, Gordon, coming into land now." Virgil must have been listening to the exchange." As soon as I've picked you up we can drop off our passengers and head for home."

"FAB." Alan sounds a lot more relaxed now. "I'll see you back at base."

Only now does my pounding heart begin to slow to a more normal level. As soon as I think I can trust my voice to sound calm, I hit the 'transmit' button to connect me to One's cockpit. "That was a good bit of flying you did back there, Alan."

"Gee, thanks Scott." Alan sounds delighted at my approval. "And thanks for your help earlier, getting me the information when I needed it."

He doesn't seem to have noticed my delay in accessing the tracking sequence. I make a mental note to put in some more practice on Five's simulator programmes. Maybe I should ask Father to schedule me up here more often?

Then again, maybe not; I don't think I could stand the strain.