These dichotomies define the Grenadines. Luxury resorts abut plywood beach bars. Sixteen-foot wooden water taxis zip among million-dollar yachts. The people on these islands seem genuinely happy, protected somehow from the inequities common to more touristed locales, the have-and-have-not nastiness that tends to muck up paradise.

The day after my circumnavigation of Union, I paddle to Mayreau, a privately owned islet of just one and a half square miles. I come ashore on a long beach called Saline and walk up the steep hill to the island's no-name village. Except for the reggae booming from one house and entertaining the whole valley, the hillside town is quiet. Modernity is a relative newcomer here. Until a few years ago, donkeys were used to carry supplies up from the bay, and a small power station brought round-the-clock electricity only in 2002. Tourists outnumber locals on most days; catamarans arrive daily from Bequia, water taxis run continuously from Union, and a Spanish cruise ship visits weekly—in anticipation of which the poisonous manchineel trees are marked with red flags, and Mayreau women sweep the beach.

From the village, a steep asphalt road wends past a handful of bars and a coral-and-stone Catholic church, to the far side of Mayreau and the sublime Saltwhistle Bay. Families pepper the beach of the protected cove, and a pair of souvenir hawkers have set up shop, offering shell necklaces and tie-dyed T-shirts. The only other presence is the elegant eight-room Saltwhistle Bay Resort, which, with its stone-and-wood bungalows scattered among neatly manicured palms, feels more like a residential enclave than a resort.

The bar at Saltwhistle Bay is open-air, with views of the Tobago Cays, where I'm headed next. The bartender whistles when I tell him of my plans. "Maybe I come with you. But…why you don't have a motor on that thing?"

Just a mile off Union Island's port town of Clifton is 135-acre Palm Island. Not so long ago, Palm was a swampy, mosquito-infested spit named Prune Island—until veteran sailors John and Mary Caldwell happened by and in 1966 arranged to lease it from the government. (Similar arrangements have seen other Grenadine islands—including Mustique, Young Island, and Petit St. Vincent—refashioned into private playgrounds.) The Caldwells irrigated the swamp with salt water (to rid it of mosquitoes) and built bungalows; John Caldwell became known as "Johnny Coconut" because of his affection for planting palms.

Elite Island Resorts bought out the Caldwells in 1999 and turned Palm Island into the all-inclusive property it is today. When I kayak up to the beach, its phalanx of chaise longues are filled with hard bodies in skimpy bikinis and Speedos. I nurse an expensive ($12.50) rum punch at its Sunset Grill while examining a stunning turquoise conch shell I picked up on the beach. I ask for help identifying it, but even the locals are stumped as to the exact species.