COLLINS AVENUE TODAY: it starts out in the shadow of oil tankers and gleaming cruise ships anchored in Miami harbor, and runs straight north along the narrow strip of land called Miami Beach. It follows the rows of run-down rooming houses, the small hotels which have seen better days, all the way up to the swanky palaces which boast their own indoor and outdoor waterfalls. The strip of asphalt looks as if it had always been there like this, connecting the world of the lonely old people who sit in their folding chairs, shivering under the winter sun, with the opulence of Bal Harbour at its northernmost end. But of courst Collins Avenue has not always been there. What was before, amazingly as late as the 1920s, was a swamp threaded with mangrove roots, with silt and seaweed catching and shrimp and snapper spawning in their curling limbs.

The beginning paragraph of Evelyn Wilde Mayerson's third novel, No Enemy But Time, immediately catches our attention, for it tells how "an enterpreneur in plus fours" dealt with this marine paradise: "With visions of polo fields, he hacked away the mangroves and covered their stubs with dirt sucked from the bay bottome. Despite losses of a few unlucky men and mules drowned while trying to escape the mosquitoes, the morass turned into a three-mile-long island of ghostly sugar whiteness, barren and sterile, until the entrepreneur hauled in topsoil from the Everglades and hired droves of stooped and patient Italian laborers, who had not heard about the mosquitoes, to set in the grass seeds by hand."

By 1941, Evelyn Wilde Mayerson tells us, Miami Beach was "a lush resort . . . including thirty-one new [hotels]. . . . They lined Collins Avenue, peculiar buildings of garnish and uncertain architecture, looking like eccentrics over the coarse coral sand."

This lower part of Collins Avenue, then, is the setting of the novel, a bittersweet tale of childhood and early adolescence, and the time is World War II. Hilary McIntyre, whose parents both work in the kitchen of the Flamingo Arms Hotel, is a thoroughly engaging heroine: innocent and precocious, heartbreakingly naive and childishly wise at the same time. With her younger brother Freddie she roams the hotel hallways and lobbies, carefully observing the guests and the young military men billeted in the hotel next door. But no, there is not a touch of Eloise of the Plaza here: this is not a snippy little girl who knows everthing. Hilary has already discovered that growing up hurts.

There is her mother, a Jewish refugee from Austria, who desperately attempts to get her mother and sister out of Europe in time. There is Hilary's Irish father, a charmer who often has trouble reconciling himself to husbandly and fatherly responsibilities. (I minded that the narrative, although often adopting the child's perspective, spoke of the parents only as Ilona and Frank -- Hilary's parents definitely are not progressive educators who would allow their children to address them in such a way, and therefore this comes through as slightly false.) There is Freddie, who is bright but slow in school, until they discover that he has trouble hearing. There is Winona, the "colored" chambermaid, so wise and honest and true that she is unforgettable. There is Hilary's soldier pen pal, who thinks that she is 22. There is Hilary's boyfriend, who demands that going steady means that she cannot be better in school than he is. There are the many guests, the servicemen, the hotel personnel, the strict teacher who breaks down when her brother is killed at Bataan, there is the soldier who attacks Hilary in the beach shack -- and then, there is also Mickey. Mickey is beautiful, she is 22; she lives in one of the hotel rooms with Mr. Radner from Philadelphia, and she falls in love with an officer trainee. But most important, she is Hilary's best friend, smoothing, explaining, protective, and sometimes impatient. The scene where Mickey tries to teach the dejected Hilary some "winning ways" to help her along in life, is one that I will cherish for a long time.

And there are others, disturbing and haunting. Hilary, as she pierces her polio-stricken frined's earlobes for earring studs. The moment when old Mrs. Portman hears about her son missing in New Guinea. The feel of Collins Avenue, where land crabs come crawling in springtime, searching for places to deposit their eggs, the females carrying the males on their backs: "Many of the crabs left the overcrowded beach and continued west . . . causing trucks and autos which crackled over them, splintering their carapaces into shards, to cut their tires to ribbons." The harrowing pages describing sailors, dead and burned, being washed up on the beach after their ship had been torpedoed offshore. "Would you get the oil out of my eyes, lady?" asked the sailor. "Of course." Ilona wiped his face with the sleeve of her bathrobe, then wiped his eyes gently with her fingers. They came back clean. There was no oil. "You didn't wipe my eyes good, I still can't see," the sailor said." (I hadn't known, having spent the war in a different danger zone, how close the U-boats really were, in 1942, to Collins Avenue.)

I was slightly mystified by the fact that the book's title failed to make sense to me: : those eager young men and women to whom the book is dedicated, they surely had an enemy more deadly than time. Their enemy was the war. But still: this is an immensely readable book for young people of all ages. It is sensitive, informed and compassionate.