“It’s not a documentary,” said Signe Sejlund, the costume designer for the Netflix limited series “The Perfect Couple.” “It’s a murder mystery.”

Yet the compulsively watchable show is not merely a murder mystery. Set on Nantucket, a glorified sand dune 30 miles off the coast of Massachusetts — where superyachts bottleneck in the harbor every summer; the median home price has surpassed $3 million; and the guy in line at Something Natural, a favorite local sandwich stand, could well be a billionaire — the show is in some sense a travelogue offering a worm’s-eye view of rich people behaving appallingly. It is also a statement on our cultural fascination with the folkways of people with too much money to count.

The series, adapted from a novel by Elin Hilderbrand, is a tale of “them” and “us.”

Embodying “them” in this case is the fractious Winbury family: patriarch Tag (Liev Schreiber), matriarch Greer (Nicole Kidman) and their three sons. Everyone else is “us.”

The Winburys have for generations vacationed at an oceanside mansion — putatively located in Monomoy, an enclave with some of Nantucket’s costliest real estate — among peers who attended the same private schools, belonged to the same country clubs and adopted the same form of garb that was once a tell for quiet wealth. Think modest A-line dresses; knotted-rope sailors’ bracelets; boat shoes so weathered they are patched together with duct tape; polos and T-shirts worn almost to transparency; and stiff Nantucket basket purses whose lids are topped with bone medallions incised like sailor’s scrimshaw.