The hordes are going. They recede after Labor Day, a honking, backed- up tide, and Route 6 at mid-Cape is again negotiable.

Some linger on, of course -- New York psychiatrists and Boston weekenders mostly. But the clam shacks and cheap efficiency cottages that line the Grand Army Highway are closing, the owners are boarding up, and the road belongs again to the natives.

Still, we stay put, with little desire to emerge like captives liberated from a siege. The tourists scarcely bothered us anyhow, separated as we are by a one-lane, weather-beaten wooden bridge and a good stretch of sandy byways. It's at the dead-end, where the pitch pines cower, that we settle in for a time. The trees, bent and stunted by winter's nor'east winds, lean against the back of the house, while the window walls to the front expose the marsh, the bay beyond and, on the horizon, the Cape's hazy grey spiral, unwinding and disappearing toward Plymouth.

Though we are not natives, we have nevertheless appropriated this spit of dune, and it is here that the family gathers at summer's end. We come to do nothing in particular -- except to watch the marsh change from its mature August greens into its autumnal reds, and to fall into synch with the tides. This place is a tidal island -- an island only at high tide, when the water rises from the mucky marsh floor and fills the lowland like a moat around a castle. When the tide's up, comings and goings are out of the question, except for waders and fiddler crabs and an occasional stranger -- no islander he -- who either knows not, or heeds not, the utter havoc salt water can wreak on a car battery.

Sometimes the flat, sandy lane leading out -- The Boulevard, we call it -- is awash for mere minutes; at other times, when the moon and winds conspire to flood the marsh, drowning even the tallest of the stalwart reeds, we must wait hours for the water to recede, to seep back into primordial ooze of the marsh's creeks and sink holes.

At times such as these, when the view from our promontory is like that from the bow of a ship, we keep our eyes peeled to the rock out there in the bay; it's our water marker, a gift the great glacier apparently left behind for those of us uncomfortable with the up-to-the-minute precision of the tide charts. The rock is an uneven gauge, but we consult it nevertheless and watch for its jagged tip as the water recedes, our cue that the road leading out is dry, at least dry enough for an excursion.

Some think all this waiting and watching is a damned inconvenience, an unnecessary capitulation to a natural law we don't have to abide -- we could move off the island, we could construct a bigger and better bridge, we could even build a helioport . . .

Ridiculous. The summer people -- from the descendants of the first squatters who play endless rounds of gin rummy in the shabby Victorian beach house up on the dune to the newcomers with their station wagons and cedar-sided pre-fabs -- would have it no other way. The islanders take a kind of solace in the rhythmic ebb and flow, a teasing game of hi-lo every 6 hours and 50 minutes. There is something humbling, yet satisfying, about living in a place where the moon is our gatekeeper.

Oh, sure, there are times when a jaunt is delayed, even cancelled, because the tide interrupts. Whims and sudden cravings for fried clams from Arnolds can't always be satisfied.

And sometimes, even we, so used to a go-anywhere, go-anytime pace, forget that the moon is luring the Earth's ocean water from shore to shore. Sometimes even we, carousing on the mainland, forget to check the lunar clock. Many are the nights when, heading toward home, we round the bend only to find our headlights reflecting a road under water; the same road that only hours earlier was dusty dry is now a salt-water pool.

We stop the car and wait, for there's nothing else to do. We step out. We listen. In the background are the cars on Route 6, rushing toward Provincetown, toward Hyannis. But closer still are the sounds of the tiny herring splashing in the creeks and the fiddler crabs -- fiddling, I suppose.

Then, suddenly, there is a stunning silence, an almost frightening stillness, the mysterious calm that occurs at the very moment the tide turns, changes course and begins to recede. It's a moment so wondrous I don't know why anyone, ever, would want to beat the tide. We may miss a concert here, a movie there, we may skip out on a friend or two, but living by the tides teaches this: nature keeps her own appointments.