Only Jumby Bay Island homeowners and guests of Jumby Bay, a Rosewood Resort, roam the two white-sand beaches of this most-exclusive West Indies islet. The low-lying, 300-acre expanse of ancient coral reef is an arm’s reach from everything Antigua has to offer, yet only a select few may take the seven-minute ferry ride back to the bay. The lucky ones stay in the 40 Rosewood rooms and villas along Jumby Bay Beach or one of 56 private homes dotting the island’s perimeter.

Novelist Ken Follett built the sev…