IF YOU'RE CHASHING after monster Humboldts, Santa Rosalía is an oceanic game park. For most of its 120 years, it was a copper-mining town, and you can still see the rusting machinery and gaping streetside mine shafts of that Dickensian time. But the mine shut down for good more than 20 years ago, and today Santa Rosalíans mine another natural resource, Humboldts, which are particularly abundant in the summer. Every night the squid come around, a fleet of more than a hundred pangas races out onto the Sea of Cortez, and Santa Rosalía's hardscrabble pangeros start handlining for Humboldts at depths of up to 1,000 feet. By morning, if luck is with them, each panga is offloading up to a ton of squid at the local processing plant. The catch is packed up and shipped to Asia, where it's a staple in local cuisine. (It's a sustainable fishery as long as the pangeros stick to handlining, says Gilly, partly because hammerhead sharks and big sport fish in the Sea of Cortez—which prey on squid—have been fished down, leaving the Humboldt to thrive.)

Down at the waterfront, Cassell, with his dive gear and cameras, is a glaring oddity, but by now the pangeros are familiar with the eccentric gringo who likes to commune with the "calamar gigante." As the Baja sun drops toward the hills, Rafael Garibaldi, whose pangas Guerito has lined up for us, mans the outboard and motors us out past the breakwater. Cassell is quiet, checking over his gear, including the restraining cables we'll use to prevent the squid from dragging anyone deep. Shawna, who's been with Cassell since 2004 and works for a plumbing-supply wholesaler when she isn't on one of his "missions," is perched in the bow fiddling with the video camera she'll use to film any topside action. And Dale, a crack spearfisherman, is jumping around in hyperactive anticipation of his first Humboldt dive. Dale is the quintessential California water rat: blond, brash, and hilarious. He's got a big whitetip shark tattooed across the back of his neck and the obligatory shark tooth hanging from a silver chain. "I'm really scared of only one or two things," he declares with mock grandeur. "Global thermonuclear war would be one. Humboldt squid would not."

We motor for 20 minutes before Rafael brings the panga to a halt. Cassell clamps two anti-mugging cables to the gunwale and throws them over the side. They drop underneath the boat, dangling to 50 feet. Another cable, this one 70 feet long, is attached to the bow, and Rafael and Guerito pull on gloves and go to work. Rafael, 50, has a deeply lined face and a drooping mustache. He throws a squid jig over the side. It's an utterly wicked-looking footlong device, fashioned from a glow-in-the-dark plug (squid are visual predators) that bristles with multiple tiers of closely spaced needles. This afternoon's mission: bring squid up on the jig for Cassell to release, so he and Dale can film them—and any trailing cannibal Humboldts—up close.

It's a matter of minutes before Rafael utters a soft grunt to announce that he's got one. He starts swinging his arms rhythmically, working to recover more than 500 feet of line. Cassell pulls his mask down over his face, rolls backwards off the panga, and disappears into the darkening water. Dale follows. They clip in; neither is wearing squid armor, trusting that the presence of more than one diver will keep the squid cautious. Rafael keeps hauling, dragging the monofilament across the gunwale, where years of fishing has burned deep grooves into the wood. The squid finally hits the surface, and even though, at about four feet, it's not a big one by Humboldt standards, I'm surprised by its heft and the defiant fire-hose spurt of water and ink that gushes into the air as Rafael pulls it clear of the surface. The squid is a deep, angry red, its arms are whipping, and its black, silver-dollar-size eyes are eerily human as they seem to appraise us. Rafael drops it back into the water, and I can see the camera lights circling underneath as Cassell and Dale film.

Rafael almost immediately hooks another Humboldt. With a slight smirk, he waves me over and offers me the line. I start hauling. After just 30 seconds, the muscles in my lower back are on fire. I try not to slow my pace, but I can't fool Guerito and Rafael, who are getting a big kick out of watching the gringo suffer for a single squid. Suddenly the line starts jerking hard, like when a bluefin tuna starts to run. "It's trying to get away," I tell them in fractured Spanish. "No," Guerito says, with an evil grin. "The others are eating it."