Rangali, often known as Madivaru or Manta Point, is at the southern end of Ari Atoll in the Maldives. I can see the light shading of the thila against the darkness of deep water below me, but I wait for the dhoni driver to tell me when to go. And when he does, it's into the water and down as fast as I can.
As usual there's a strong current. The long reef passes me like an express train.
I have a momentary encounter with a large hawksbill turtle but there's no chance to dally. I am still wiping away the bubbles that cling to the front port of my camera and sorting out my twin flashguns when the first spaceship hoves into view.
Manta is the Spanish word for cloak, and this animal is well-named. One of the largest a diver will commonly encounter under water, it is also one of the most spectacularly graceful.
This one moves effortlessly against the flow and I am swept past it and onwards down the reef.
I look for a particular spot. I know it well. There's a trench-like indentation across the top of the reef and I drop down into it, putting the brakes on by sticking my reef-hook like a dagger into a convenient hole in the sub-strate.
Down here, I can duck out of the flow and watch for oncoming mantas as they bide their time, like so many aircraft, out in the gloom.
Suddenly one is upon me. It hovers overhead, blotting out the blue sky that ripples through the surface above. The gentle giant glides effortlessly against the current as dozens of tiny fish, all manner of different types of wrasse, gather up from the reef under its wings.
They dart in and out of its gill-slits, like so many service technicians working under a great airliner.
This is a manta's cleaning station, and I am lying under it. Another big animal arrives and starts a queue. It patiently waits and contents itself by doing a few barrel-rolls, its mouth agape, feeding on the plentiful plankton that spoils the clarity of the water, guiding the food in with its unfurled lobes.
The first manta moves off and the next is in place, this one adorned with twinned remoras; missiles underslung on its delta wings. Its big black eyes have a certain knowing look. These animals are used to meeting divers.
Then there is another manta, and another. Trying for that elusive wide-angle close-up shot, I raise myself too far from the protection of my trench and am lifted by unseen hands. I am taken by the never-ending flow of plankton-rich water that rushes from inside the atoll and sent irresistibly onwards down the reef top.
I get the hook tucked in again and manage to stop before I'm sent off into midwater at the reef end, and then I'm tethered, flying like a kite.
But it's only for a moment, while I pause to rethink my plan.
Five, six, now seven cloaked behemoths have passed me and are queuing up at the cleaning station, but I am agetting nothing but rear views in the planktonic haze.
I drag myself down over the edge of the reef and laboriously pull myself back along it half a metre at a time, sticking my hook into solid rock where I can.
I'm careful to stay below the level of the mantas, my exhaled air bubbles swept away from me horizontally in a way that does not disturb them.
And once I think I'm far enough upcurrent, I swim the few metres that take me back on top of the reef and allow myself to be swept back down towards my quarry, camera ready for those important head-on shots.
This exercise is repeated two or three more times until I am out of film. Then, as usual, something very special happens.
Two mantas wheel and roll, cavorting and pirouetting together, belly to belly, in a graceful, synchronised ballet.
It's as captivating to watch as it must be to participate. These two majestically sensuous animals are engaged in a mating ritual which I am able to witness, mesmerised and shameless.
THE MANTA RAY
Manta biriostris, the largest of the rays, is part of the elasmobranch family of cartilaginous fishes that includes sharks. A plankton-feeder, it filters water through plates on its gill openings. Pan-tropical, the largest can weigh-in at up to 2000kg.
Usually white on the underside but with dark patches often covering the upper side, the manta ray has large feeding flaps or lobes which it can carry rolled up so that they look like horns. It can deploy them to direct food into its cavernous mouth. The smaller but otherwise similar mobula ray does not have these large flaps.
A true pelagic species, the manta is often found drawn in numbers to its food source at the entrances to underwater channels, where plankton-rich water from an atoll's tropical lagoon empties into the ocean.