In the months leading up to the hunt, Dylan Mayer trained twice a week in his parents’ swimming pool, asking friends to attack him, splay their arms and grab him, drag him to the surface and shove him below it, pull off his mask, snatch his regulator, time his recovery. By last Halloween, he was ready, and as the light began to fade that afternoon, the broad-shouldered 19-year-old jumped into a red Ford pickup truck with his buddy and drove some 40 minutes from Maple Valley, Wash., to West Seattle. They arrived at Alki Beach around 4 p.m., put on their wet suits and ambled into Cove 2. Then they slipped into Elliott Bay, the Space Needle punctuating the city line in the distance like an inverted exclamation point.

Under the dark water, the teenagers looked around with the help of a diving light. At 45 feet, they passed a sunken ship, the Honey Bear, and at 85 feet, beneath the buoy line, they saw further evidence of the former marina — steel beams, pilings and sunken watercraft. Marine life thrived in this haven of junk, and for this reason, Cove 2 was a popular dive site. According to the permit he had just purchased at Walmart, Mayer was allowed to catch this sea life and cook it, which is exactly what he set out to do. He wasn’t much of a chef, but he had experience foraging for his dinner. Mayer had attended a high school known for its Future Farmers of America program; he also knew how to slaughter cows and castrate bulls. Now he was going to community college, where he was asked to draw something from nature. He figured that he might as well eat it too. And as he scanned the bay, he could already imagine searing the marine morsels on high heat and popping them, rare and unctuous, into his mouth. He soon spotted his prey. “That’s a big [expletive] octopus,” he scribbled on his underwater slate.

The giant Pacific octopus was curled inside a rock piling, both its color and texture altered by camouflage. Mayer judged it to be his size, about six feet, and wondered if he could take it on alone. He lunged at the octopus, grabbing one of its eight arms. It slipped slimily between his fingers, its suckers feeling and tasting his hand. He reached for it again, and again it retreated. Able to squeeze its body through a space as small as a lemon, the octopus was unlikely to succumb to his grip. He poked it with his finger and watched it turn brighter shades of red, until finally, it sprang forward and revealed itself to be a nine-foot wheel charging through the water.