About a hundred miles off the coast of Thailand, three dozen Cambodian boys and men worked barefoot all day and into the night on the deck of a purse seiner fishing ship. Fifteen-foot swells climbed the sides of the ship, clipping the crew below the knees. Ocean spray and fish innards made the floor skating-rink slippery. Seesawing erratically from the rough seas and gale winds, the deck was an obstacle course of jagged tackle, spinning winches and tall stacks of 500-pound nets.

Rain or shine, shifts ran 18 to 20 hours. At night, the crew cast their nets when the small silver fish they target -- mostly jack mackerel and herring -- were more reflective and easier to spot in darker waters. During the day, when the sun was high, temperatures topped 100 degrees Fahrenheit, but they worked non-stop. Drinking water was tightly rationed. Most countertops were crawling with roaches. The toilet was a removable, wooden floorboard on deck. At night, vermin cleaned the boys' unwashed plates. The ship’s mangy dog barely lifted her head when the rats, which roamed on board like carefree city squirrels, ate from her bowl.

If they were not fishing, the crew sorted their catch and fixed their nets, which were prone to ripping. One boy, his shirt smudged with fish guts, proudly showed off his missing two fingers -- severed by a net that had coiled around a spinning crank. Their hands, which virtually never fully dried, had open wounds, slit from fish scales and torn from the net’s friction. The boys stitched closed the deeper cuts themselves. Infections were constant. Captains never lacked for amphetamines to help the crew work longer, but they rarely stocked antibiotics for infected wounds.

Disobedience was less a misdemeanor than a capital offense.

On boats like these, deckhands were often beaten for small transgressions, like fixing a torn net too slowly or mistakenly placing a mackerel into a bucket for sablefish or herring. Disobedience was less a misdemeanor than a capital offense. In 2009, the U.N. conducted a survey of about 50 Cambodian men and boys sold to Thai fishing boats. Of those interviewed by U.N. personnel, 29 said they witnessed their captain or other officers kill a worker.

The boys and men who typically worked on these ships were invisible to the authorities because most were undocumented immigrants. Dispatched into the unknown, they were beyond where society could help them, usually on so-called “ghost ships” — unregistered vessels that the Thai government had no ability to track. They usually did not speak the language of their Thai captains, did not know how to swim and, being from inland villages, had never seen the sea before this encounter with it.

Virtually all of the crew had a debt to clear, part of their indentured servitude, a “travel-now, pay-later” labor system that requires working to pay off money they often had to borrow to sneak illegally into a new country. One of the Cambodian boys approached me and, deeper into our conversation, he tried to explain in broken English how elusive this debt became once they left land. Pointing to his own shadow and moving around like he was trying to grab it, he said, “Can’t catch.”

This was a brutal place, and one that I spent five weeks in the winter of 2014 trying to visit. Fishing boats on the South China Sea, especially in the Thai fleet, had for years been notorious for using so-called sea slaves, mostly migrants forced offshore by debt or duress. The worst among these ships were the long-haulers, many of which fished hundreds of miles from shore, staying at sea sometimes for over a year as motherships provided supplies and shuttled their catch back to shore. No captain had been willing to carry me and a photographer the full distance, more than 100 miles, out to these long-haul boats. So, we instead hopscotched from boat to boat – 40 miles on one, 40 on the next, and so on – to get out far enough.

As I watched the Cambodians, who, like some water-bound chain gang, chanted to ensure synchronicity in pulling their nets, I was reminded of an incongruity that confronted me time and again over several years of reporting offshore. For all its breathtaking beauty, the ocean is also a dystopian place, home to dark inhumanities. The rule of law -- often so solid on land, bolstered and clarified by centuries of careful wordsmithing, hard-fought jurisdictional lines, and robust enforcement regimes -- is fluid at sea, if it’s to be found at all.

There were other contradictions. At a time when we know exponentially more about the world around us, with so much at our fingertips and but a swipe or a tap away, we know shockingly little about the sea. Fully half of the world’s peoples now live within a hundred miles of the ocean, and merchant ships haul about 90 percent of the world’s goods. Over 56 million people globally work at sea on fishing boats and another 1.6 million on freighters, tankers and other types of merchant vessels. And yet journalism about this realm is a rarity, save for the occasional story about Somali pirates or massive oil spills. For most of us, the sea is simply a place we fly over, a broad canvas of darker and lighter blues. Though it can seem vast and all-powerful, it is vulnerable and fragile in part because environmental threats travel far, transcending the arbitrary borders that mapmakers have applied to the oceans over the centuries.

Like a dissonant chorus in the background, these paradoxes captivated me throughout my journeys spanning 40 months, 251,000 miles, 85 planes, 40 cities, every continent, over 12,000 nautical miles across all 5 oceans and 20 other seas. Those travels provided the stories for this book, a compendium of narratives about this unruly frontier. My goal was to report not just on the plight of sea slaves, but also to bring to life the full cast of characters who roam the high seas. They included vigilante conservationists, wreck thieves, maritime mercenaries, defiant whalers, offshore repo men, seabound abortionists, clandestine oil-dumpers, elusive poachers, abandoned seafarers, and cast-adrift stowaways.

Since I was young, I’ve been enchanted by the sea, but it was not until one brutally cold Chicago winter that I acted on my fascination with this vast unknown. Five years into a doctoral program in history and anthropology at the University of Chicago, I decided to procrastinate on completing my dissertation by fleeing to Singapore for a temporary job as a deckhand and resident anthropologist on a marine research ship called the RV Heraclitus. For three months, the whole time I was there, the ship never left port due to paperwork problems, and I spent the time getting to know the crew from other ships docked nearby.

This stranded stint portside in Singapore offered my first real exposure to merchant seafarers and long-haul fishermen, and the experience left me riveted by what seemed like a transient tribe of people. These workers are largely invisible to anyone leading landlocked lifestyles. They have their own lingo, etiquette, superstitions, social hierarchy, codes of discipline, and, based on the stories they told me, catalogue of crimes and tradition of impunity. Theirs is also a world where lore holds as much sway as law.

What became especially clear in these conversations is that moving freight by sea is much cheaper than by air partly because international waters are so uncluttered by national bureaucracies and unconstrained by rules. This fact has given rise to all manner of unregulated activity, from tax sheltering to weapons stockpiling. There is, after all, a reason that the American government, for instance, chose international waters as the location for disassembling Syria’s chemical weapons arsenal, for conducting some of its terrorism-related detention and interrogation, and for disposing of Osama bin Laden’s body. Meanwhile, the fishing and shipping industries are as much victims of offshore lawlessness as they are beneficiaries and perpetrators of it.

I never finished my dissertation. Instead, I took a job in 2003 at The New York Times, and over the next decade, as I learned how to be a reporter, I occasionally and unsuccessfully pitched the notion of doing a series about this offshore world. I leveraged every persuasive comparison I could muster. An all-you-can-eat allegory buffet, the seas offer inestimable journalistic opportunity, I argued. From a story-telling perspective, this two thirds of the planet is virgin snow, I contended, because few, if any, other reporters are comprehensively exploring it.

In 2014, Rebecca Corbett, my editor at that time, agreed and in embracing the proposal, she wisely nudged me toward focusing more on the people than the fish, delving primarily into the human rights and labor concerns, as the environmental issues would arise, as well, through that lens. The first story from the New York Times’ Outlaw Ocean series ran in the paper in July 2015, with an additional dozen or so pieces published in the subsequent year. I took an additional 15-month leave from the paper, starting in January 2017, to continue reporting for this book.

During my travels, I had a lot of downtime, which I spent immersing myself in books about the ocean. Experientially and philosophically, the sea is and has always been many different things to different people. It is a metaphor for infinity and a place of the purest form of freedom, distinctly divorced from government meddling. An escape for some, the sea is also a prison for others. Full of devouring storms, doomed expeditions, shipwrecked sailors and maniacal hunters, the canon of sea literature offered a vibrant picture of a watery wilderness and its untamed rogues. Like birds on the Galapagos, these men, over centuries, had done mostly as they pleased, evolving largely without predators. The surprising fact is that they still do. My hope with this book is to offer a sketch that brings into the present our awareness of these people and this place.

To make the book more of a first-person travelogue (“Tell stories, don’t write articles,” my editors used to remind me.), I tried to rely less on shore-side interviews or archival testimonials than reporting from the ships themselves. Mostly, these were fishing ships but also cargo vessels, cruise liners, medical boats, floating armories, research and advocacy ships, as well as navy, port police, and coast guard cutters.

As a writing project, there was real risk in tackling such an ambitious topic -- or, as the expression goes, trying to "boil the ocean." At times, the reporting process was so zigzagging that it felt less like journalism than an attention deficit disorder. But the more I traveled, the more one story led to another -- none of them neat or tidy, none of them split clearly between right and wrong, villain and hero, predator and prey. Like the oceans themselves, the stories that emerged were too sprawling to force into a single, straight-line narrative. So, instead, I organized the chapters as a series of essays, confident that readers would connect the dots in their own ways, beyond the patterns I spotted.

In the end, the goal of this project is to bear witness to a world rarely seen. It recounts a maritime repo man spiriting a tanker from a Greek port into international waters, and a doctor clandestinely shuttling pregnant women from Mexican shores to the high seas to administer otherwise illegal abortions. It chronicles the work of vigilante conservationists, who in the South Atlantic Ocean chased Interpol’s most wanted poacher ship and then in the Antarctic hunted and harassed Japan’s last factory whaling ship. In the South China Sea, I landed in the middle of an armed standoff between two countries, each of which had taken hostages from the other. Off the coast of Somalia, I found myself temporarily stranded on a small wooden fishing boat in pirate-infested waters. I saw a ship sink, rode out violent storms and watched a near mutiny. Reporting these stories took me from a submarine in the Antarctic and South Atlantic Oceans, to offshore weapons depots in the Gulf of Oman and to oil platforms in the Arctic and the Celebes Sea.

For all that adventure, though, the most important thing I saw from ships all around the world, and have tried in this book to capture, was an ocean woefully under-protected, and the mayhem and misery often faced by those who work these waters.