It’s still dark, but the birds, dozens of them, have begun to sing, and they must know something. It’s time for him to stop, to find a place to shelter for the daylight hours. He takes a notebook out of the back pocket of his shorts and marks his location. The scent he found earlier, mixed in among the more common smells of raccoons, coyotes, dogs, humans, and a single mountain lion, had unwound from a notch in the bark—sharper than salamander, muskier than sowbug, with overtones of freshwater mollusks. Three in a row he has found now, the most hopeful sign yet. It must be someone who, like him, has not yet metamorphosed.

A few cars hustle along the wide streets on either side of this thin strip of park, but the park itself is mostly deserted, and in any case, in the dark, at least from afar, he looks just like a man.

He picks his way across the grass, its blades (he can feel each one) poky and cool under his feet. A few coyotes watch him from the eucalyptus across the way, but he’s not afraid of them. He is as tall as a tall human, and they will leave him alone. To coyotes and dogs he smells like nothing, like leaves or a mushroom buried underground.

He finds a tree, a tall one with thick branches and a round canopy that encloses the space underneath like a cozy tent. As he climbs, the leaves rustle and move aside for him. His green shape will blend in perfectly here. No one will notice his mottled skin or his large yellow eyes with the vertical pupils, good for seeing at night.

A few branches above him, a brooding parent sits on an egg, eyeing him but remaining soundless. He has to avoid only scrub jays, who tend to screel at the sight of him, as if he were a hawk they need to warn others about.

He crawls out over the limb, jouncing it a little, finding a secure crook. Once he’s comfortable, he will enter a state of hibernation and let his temperature drop, and then he will become so still that not even the birds and spiders will notice him. But as he stretches himself out, a thorn scrapes his arm and he feels his flesh separate and bleed. What to do now? He can wait till night comes again, or he can find something to wrap it in sooner, though traveling in the daytime is risky. He should have known to follow the cornflower-blue butterflies long ago, when they moved away.

He will stay here for now, in this tree, which he senses has sheltered a variety of creatures passing through. Earlier, he pursued a different idea and climbed a building near the final scent mark. In one of the windows, even in the middle of the night, there was a light on. (At any hour, someone is always awake.) He tapped at the window, and the person looked up but did not see him, despite his yellow eyes and the glowing spirals on his skin.

Over time he has developed a sense for this, for who is and who is not open to him. Often the ones who see him are searching for something too.

Gina Lee exits her building near the San Francisco Panhandle, a white terrier in tow on a blue leash. It’s a sunny morning in mid January, just after eight, and a square recycling truck is grumbling its way up the block. As Gina threads through the emptied bins on the sidewalk, feeling her way forward in her soft gray dog-walking sneakers, her phone dings. It’s Mark.

Also need to pick up Tom’s clothes.

Right. Tonight is the engagement party, and Tom refused to take the clothes with him all the way to Disneyland and back.

Three wavering dots appear on the screen as Mark types. In front of her, blue bins ascend into the air. Glass bottles, cardboard cartons, and tin cans rattle into the truck, a few wafting sheets of paper following them down. She reads:

An engagement party and Paris too? As if engagements need honeymoons. But it’s not permanent, only six months.

Six months—it might as well be an eternity! A hollowness gapes under her ribs; that prickly spinning, she knows it’s another burst of loss. But what does it matter to her now where Mark lives, whether it’s here or across the world in Paris? She lets her vision blur until she feels the tug of the leash: Nimbus trying to get to the next tree.

It seemed bearable before, knowing they were out there, south-ish, east-ish, near Duboce Park, in Kim’s third-floor apartment with street views that Gina saw once at one of Mark’s work parties. But now he’s changing the situation on her again. It’s as if she were an oyster and every time a new piece of grit gets into her shell she has to work at it all over again, glossing over the sharp points with nacre to stop them poking her. Paris, of all places! They went there as a family once—sun and white bridges.

She types back with her thumbs.

Perfect. Everything for Mark is perfect. He can’t even tell that she’s annoyed. And now he’ll rummage through the apartment and make a huge mess that she’ll have to clean up! But no, that’s not fair, in fact Mark is pretty neat. If he had sneaked in and picked up the headphones, she might not have known at all.

“Come on,” Gina says, watching Nimbus sniff at a red and white fire hydrant. “Let’s go to the park.”

But now another dog is approaching, and they are close enough to home for Nimbus to stand tall and straight, guarding the sidewalk, preparing to bark. Gina remembers how her children, Carlie and Tom, filmed him barking, catching in slow motion the opening and shutting of his butthole, rolling with laughter over the video, the two of them.

Moments like that, and so many others she has stored up—dancing by the window of a friend’s apartment at New Year’s, or waking before dawn to catch a view of a comet, or carrying a baby to bed to nurse, deep in the night, the warm dense heft, that heaviness of a baby, wrapped in a fleece sleeper. She has a treasure trove of moments like that, in which Mark doesn’t figure at all. She should never let herself forget that.

The other dog turns away, and Nimbus gives a soft, superfluous, satisfied bark.

As they near the corner, a gate bangs open and Estelle emerges, crossing the street at a diagonal, headed to her car. Gina freezes and steps closer to the wall. The neighbors call Estelle “the crazy lady.” She bumps into things with her car; her blue sedan is covered with dents. Gina had a peaceful relationship with her for years, but after Mark moved out and went to live with Kim, Gina protested once when Estelle said something about Nimbus, and now Estelle views her as an enemy. She revs through the intersection whenever Gina is crossing the street and shouts, “You’re a jerk!” Last week, when she passed Gina on the sidewalk, she yelled into her phone, “They eat dogs!” and then repeated it: “I said, they eat dogs!” Gina was confused at first, then realized Estelle was talking about her.

Gina tiptoes, keeping a thin but leafy sapling between them. “Let’s go,” she says to Nimbus. Nimbus looks at her sideways and dodges a somersaulting leaf. They go on.

Mark will be in the apartment soon. One day she’ll need to change the locks. What does he think, picking up the key—wherever he keeps it now, still on his keychain or somewhere else—feeling the size and shape and weight of it? The key to his home for twenty years. But what’s the use of thinking about that. A better question is why does he lose things all the time, keys, credit cards, these noise-canceling headphones for airplanes. Everyone drop everything and help search! What a relief that it’s no longer something she has to worry about. But then, strangely, she feels a pang, even for that.

Gina and Nimbus cross the wide busy street and enter the Panhandle itself—the thin, nine-block-long, one-block-wide strip that sticks out from the rest of Golden Gate Park and gives the neighborhood its name. They pass a woman and her dog, a familiar pair: curly-haired woman, gray-brown dog. This is the woman who called out to Carlie, “How’s your mean brother?” with a smirk. What had she seen or overheard?

Gina and Nimbus cross the bike path and enter the empty area next to the basketball courts, where on weekends people assemble for tai chi (her mother, visiting, sometimes joined them), or boxing, or to twirl batons or swing wooden swords. It’s cold at this hour, and her fingers are half frozen, but what difference does it make? It wouldn’t matter if they fell off. Nimbus sniffs at a curled-up leaf on the ground, and Gina waits, pivoting in a circle.

Each of her family members is on an individual odyssey now, their routes intersecting in the past and again in the future. She is looping from home, around the Panhandle and back. Tom is a boomerang, flung to Southern California with the Autonomy High School band, soon to sling back at a ferocious pace. Carlie is launched further, to college on the East Coast, and who knows whether she will bend her way back or only head further out. Gina envisions the Solar System, and those spacecraft with delicate antennae that were hurled from Earth decades ago and finally, she read, escaped the Solar System entirely. Gone. Soon they won’t be able to report back anymore and will just go on, flying past star after star, through unnamed places where no one has ever been or will ever go. And then there’s Mark. Once they revolved around each other; now the ties have snapped and they are spinning apart, and she knows less and less about his comings and goings. The kids occasionally reveal something, offer up tiny, staggering fragments of his life, but that’s all. Mark, always on the move, headed toward the next thing, while she lingers here, one little spot in the middle of the Panhandle.

She toes an acorn, one of dozens on the asphalt, squeaking the sole of her sneaker on the ground, sending it skittering across the way. In a few steps, she’s at the next acorn; this one she sends a foot into the air before it drops and bounces and rolls to a stop.

What she can’t stand is the unfairness of it. Mark is so happy, carefree, care-less. Whenever she sees him, when he comes by to pick up something or take Tom somewhere, he seems to amble, hands in his pockets, maybe even humming a tune. He is going on with his life; he is happy.

Of course he’s happy, throwing parties and running around town with Kim, who rock-climbs, who likes fancy restaurants and knows the city’s celebrity chefs (Kim talked about this at that work party years ago). Mark is doing all of these things and sleeping with Kim, cuddled in a bed covered in billowy sheets, a mound of soft joy.

The gaze Kim beamed at him that time at the all-company picnic, head tilted up, so admiring. Kim’s tight ponytail, thin face, not particularly beautiful but young and youthfully hopeful, expecting only good things from life. There was a respectable distance between them then, but Gina felt the invisible force lines tugging them toward each other. They must have felt it too and had to resist, at least that day. But then they didn’t resist, and—she can see it, Godzilla stomping down their street, waving a tail, knocking buildings to smithereens. And now she is left behind in the rubble, the wasteland.

She doesn’t have to think of it this way, but she can’t help it—rubble, rubble, rubble! A smoldering mass twists slowly in her chest as she thinks of Kim, with her ponytail. But it isn’t Kim’s fault; Mark is the one she’s angry at. All those years of Mark sitting blandly on the couch with his legs stretched out, and then he thinks he can just get up and leave forever. It makes her want to grab his shirt and rip! But no, how embarrassing, better to do what she has done a million times since Mark left—burn the thought of him cleanly away, a sudden flame blazing over a paper image, turning him to a crisped silhouette that crumbles into ash for the wind to blow away.

What will she do? What can anyone do, when someone has left? She has a special day planned too. Mark is getting engaged, but she will get in touch with Peter. She can’t forget Peter; there was that kiss, or half-kiss (so embarrassing). She can see where that goes.

A pair of bicycles whizz by, ringing their bells, their flashing taillights disappearing down the path. Above, tall eucalyptus trees tilt in the wind. A gust blows at her and Nimbus, pushing her hair back and sleeking the fur around Nimbus’s face, making him squint and look, for a moment, like a small bear.

It seemed natural at first for Mark to go on his long night walks after his mother died. He no longer cried, but every evening, once the day’s tasks were done, he would lift his jacket from the coat-rack, put on his old sneakers with the toe holes, and go. At first she would wait up for him, worrying that he had gotten lost, staying awake by sitting up in bed and leaving the light on. But then it became part of the household routine, and she let him do what he wanted to do because who knew what it would take for him to feel normal again after Shirley died that way?

So it was a surprise when, six months ago, he dropped it on her: Kim, yes, the one from work. And then everything happened so quickly—right away, in fact. He had it all planned and left immediately. He must have packed a suitcase ahead of time without her noticing, or maybe, long before that, he had begun to move things over, sock by sock, shirt by shirt, to Kim’s place, so that he could leave unencumbered. Gina barely responded when he told her; she couldn’t believe this was happening to them, to her! Only later did the hurt, the fury, bubble and boil. If she had found the right words…but could words have stopped it? Some time ago, she doesn’t know how far back, she stopped believing in trying to change people’s minds.

After that, irregularly, every few days or once a week, more stuff would disappear, and though she should have become used to it, she felt hurt each time. His big computer monitor disappeared, leaving the wall behind it a shocking white, scuffed by mysterious pencil marks. Gaps in the closets, gaps on the bookshelves, books tipping into empty spaces this way and that. She, meanwhile, banged her fists on couch cushions, ripped up photos. She even threw a plate one day when he came to pick up his tennis racquet, but that had been pleasing only for a moment; the plate cracked dully into two big pieces instead of exploding in shards the way she had hoped, and then Mark just left and there was a mess to clean up.

A print from the living-room wall disappeared, and she replaced it with a “Bloomsday in New York” poster that her brother Chris had given her, that had been taking up space in the closet forever. In her bedroom, where something else had disappeared, she put up a Winnie the Pooh picture that her father had given to Carlie when she was born. It would be hopeless to try to explain to anyone why she has a Winnie the Pooh poster in her bedroom now. She laughs to think of it. But it was one of the last gifts her dad bought anyone. The caption says, “Let’s all be friends!”

She and Nimbus walk past the playground, which is under construction now, a giant sand pit, then wind along the path under the trees. A pack of runners goes around them; strange birds chitter. Nimbus pulls toward a tree, a broad one with a curved canopy whose outer branches are so low that Gina has to duck. Underneath, the air is quiet and humid.

Just as she straightens up, a green streak flies up the tree’s trunk and crashes through the leaves. Green but the wrong green, too bright. Nimbus, head raised, barks up at the leaves. Gina looks into the branches but sees only dark lines of woody bark and shadowed leaves flipping back and forth in the wind. A bird, maybe? It was too large to be one of those parrots descended from escaped pets, green with a bit of red, that appear overhead in sudden wild flocks, conversing in their tropical voices. Could it have been a person in costume? But it was too fast and too high to be one of those circus students who come to the park and tie colorful slacklines from tree to tree to practice tightrope-walking in the sun. A trapeze artist?

Looking up, she feels the weight of eyes on her but sees nothing. Her imagination, then. A small bird, plain and tan, swoops in a parabola from tree to grass, then takes off again into the sunlight.

But the colors shift at the edge of her vision. There is something scurrying—no, slinking and sliding across a branch six feet above her. She can’t see it, camouflaged in the shadows, but the size of the disturbance and the creaky jounce of the thick branch suggest that it’s large. She thinks of a monstrous ostrich-like bird, then a snake—a python—then a leopard.

In the dark leaves above, a pair of golden eyes appears.

“Is that an owl, Nimbus?” Gina says. Owls have large golden eyes.

But these eyes are framed in a face roughly human, painted in mottled green patches that glimmer in the leaves and shadows. Camouflage. It must be some sort of war game, Gina decides, as she discerns a body hunched on the limb. Still she takes a step back, knowing that she hasn’t accounted for the golden eyes.

Frozen with fear and curiosity, her body twitching with every thump of her heart, Gina peers up at the branch while Nimbus sniffs at the tree’s trunk, oblivious or indifferent to the figure in the leaves. Her eyes adjust, and she can make out a little more—a sharp shoulder and what seems like an arm, shadowed but painted with the same colors of camouflage.

He is motionless, as if he hopes to remain hidden. But his golden eyes, open in slits, shine with a small light, and Gina gazes directly at them long enough to show that she has seen him.

He blinks. Now what? Gina considers asking, “What are you doing up there?” or “Are you hiding from someone?” But before she can decide what to say, an arm separates from the leaves and emerges out of them, lowering from the branch. The hand is cupped around something, and Gina leans closer to look. It looks like a pale scraggly feather and a kiwi.

Before Gina can take the objects from him, if indeed he was offering them to her, the arm retreats quickly, like a drawbridge snapping shut.

Another rustle, and he seems to withdraw. Gina follows the gold glint of his eyes into the leaves. They disappear, leaving two dark spots in her vision. He must have blinked again. This time he doesn’t reopen his eyes, and she searches the mass of leaves, going over them bit by bit, once, twice, three times. She can’t find any part of him.

So strange. Was it a person? What was he doing there?

All the leaves flutter noisily in a sudden breeze, as if the tree has been picked up by its trunk and shaken. Gina looks into the branches again, then walks around the trunk. But there is nothing, just sticks and leaves. He’s gone, if he was ever there to begin with. It must have been an owl after all, she thinks, and now it has flown away (that was the leaves shaking) or hidden itself in the branches.

Did she really see that face, that hand? Unlikely.

She looks at Nimbus. “Did you smell anything?” she says.

But he’s sniffing at the bark. All he cares about is other dogs.

MIGRATORY CREATURES follows 47-year-old Gina Lee through a single January day that is both ordinary and extraordinary. Gina’s estranged husband, Mark, who left her six months earlier for his new girlfriend, is celebrating his engagement at a party that night. A still-adrift Gina muddles through the hours of this difficult day, wanders around San Francisco, tries to start a romance with awkward electrician Peter, and then encounters, at her kitchen window, a strange and appealing amphibious man who just might give her everything she needs. Before Gina can truly move on, though, she must make sense of the breakup of her marriage, as well as the disaster that preceded it, a suicide that continues to haunt her family.

My novel had two major inspirations, James Joyce’s Ulysses and Rachel Ingalls’ Mrs. Caliban. The structure of MIGRATORY CREATURES is modeled on Ulysses, with a chapter for each hour of the day. Like Ulysses, it employs occasional “experimental” forms. Some sections are modeled explicitly on those of Ulysses—for example, a chapter that uses a “question-and-answer” format is based on Joyce’s Ithaca episode. And, like Ulysses, the final chapter consists of a woman lying in bed, thinking about her life in a stream-of-consciousness style. Other experimental forms in the novel are my own, including a “Top 10” list of things that Gina learned from her mother-in-law and a section in graphic-novel format.

The amphibious man, Oliver, is a literary descendant of a similarly green and mottled character in Mrs. Caliban. Like the protagonist in that novella, Gina finds (or perhaps invents) her amphibious man right when she needs him most. The main themes of MIGRATORY CREATURES are love, loss, imagination, family, and the inevitability of change over time.