"They won't bite!" Leo assures us, to the enormous relief of the beautiful British couple from Sarf Lunnon, who are clearly out of their depth - although only metaphorically, as the crystal-clear water's just waist-deep.
Colourful fish, big and little, dart through the coral, the parrot fish rasping at it with a sound like ripping Velcro. The numbers aren't huge, but there's plenty of variety, including velvety-lipped giant clams.
The next little island is Moturakau, which featured in the Survivor: Cook Islands TV series. I follow the Beautiful Brits along the path across the middle. It's yet another challenge for them, after being worried by the jokey snorkelling briefing about clams biting fingers off ("What's a clam look like? How will I know?"). White terns nesting in the mahogany trees squawk above us, and a few spider webs drape across the path. "I can't do this!" she says, panicking at all this raw nature: this pair are prime Survivor material. They follow me as I doughtily break through the webs, and she falls exhausted on the sand on the other side while he checks his phone.
Our last stop is a stunner: the sandbar next to One Foot Island, a sweep of white sand lapped by the clearest water, star of countless tourism advertisements and private wedding videos. Beyond is the white ruffle of breakers on the reef, and beyond it the deep blue Pacific. Left and right are cartoon-classic islands with waving coconut palms. There are worse places to begin a life together.
We wade lazily to the island where Leo and his shipmates have set up lunch in a thatched hut, salads on the table, tuna, wahoo, sausages and bananas sizzling on the barbecue. After grace, we feast, and the chickens come running. The Cook Islands national bird, they're everywhere, seizing on dropped breadcrumbs and bits of fish.
Leo, not only captain and cook, but also minstrel, plinks away on his ukulele as we eat. Afterwards our passports are stamped with the One Foot logo, something to make future immigration officials pause enviously as they rifle through the pages.
Then it's time for more gentle wallowing in the water, rolling with the little waves like the sea slugs on the bottom, and just as energetic, marvelling at the warmth and the beauty.
All too soon, we have to head back, puttering quietly across the beautiful lagoon in all its spectacular glory while Leo sighs about missing out on the job he was after at his mate's petrol station. He looks at the sparkling water, the low palm-fringed atolls, the surf breaking on the reef and says wistfully, "I'd rather be in New Zealand."
Back on our resort balcony, as the sun drops into the sea in a display of pink and gold, we raise our glasses to the fact that we're not. Dinner is at Tupuna's Restaurant. It's an Aitutaki classic in a private garden, an open-sided room surrounded by fragrant tiare bushes. Mosquito coils burn at our feet, a ginger cat sits on the step and lizards chirp on the ceiling. The welcome is friendly and the food is delicious: the evening's special is mud crab, its presentation magnificent and its sweet meat worth the effort of extraction.
Back at our beachfront villa, there's only one way to end such a perfect day: to stand on the sand in the dark and marvel at the stars, the Milky Way a splash across the blackness and showy Scorpio sprawling, claws hooking the horizon. The breeze is warm and little waves lap invisibly on the sand, creeping up the beach to erase today's footprints for another flawless start tomorrow.
CHECKLIST
Getting there: Air New Zealand flies from Auckland to the Cook Islands six times weekly and often offers special deals. Fly to Aitutaki with Air Rarotonga: a good day trip, but far better is to stay.
Where to stay: There's a range of accommodation: highly recommended is Pacific Resort Aitutaki.
What to do: For the lagoon cruise: Bishops is smaller, the Vaka looks more traditional - both offer almost the same experience.
Pamela Wade visited the Cook Islands at her own expense.