It was supposed to be his last day of filming in Nova Scotia, and James Cameron realized something had gone awry. Standing in the middle of the set he had been working on for weeks, he couldn’t find his way out. He was feeling “suddenly and very distinctly woozy.” By the end of the night, there would be crew members conga dancing and racing wheelchairs through a hospital corridor. And the chowder was to blame.

Of all the legends that have grown around the production of Titanic, at the time the most expensive movie ever made, the case of the poisoned chowder is the most spectacular—all the more so because it remains an unsolved mystery. Twenty years after Titanic opened in theaters, no one knows for sure who laced the chowder with P.C.P., or why.

It was the night of August 8, 1996, and the cast and crew of Titanic—including Cameron, producer Jon Landau, cinematographer Caleb Deschanel, and stars Bill Paxton and Suzy Amis—were ready to wrap up the scenes set in the present-day and move on to Mexico, where a massive reproduction of the doomed ship was waiting on an outdoor soundstage in Baja. Filming at night in Shearwater, just across Halifax Bay, the crew broke for “lunch” around midnight; a local catering company had provided, among other options, chowder.

The precise nature of this chowder has been lost to time. Cameron says it was mussel chowder; Paxton said in 2015 it was clam; the Halifax Police report at the time determined that it was lobster. Whatever the chowder was, Suzy Amis was one of the few who wasn’t interested; Cameron, now married to Amis, notes “she’s always been high on my list of suspects as a result.”

For the more than 60 people who did eat the chowder, it didn’t take long for the effects to take hold. Cameron, who initially thought the shellfish might have contained “paralytic shellfish neurotoxin, which is very dangerous,” immediately stepped away from the set to vomit. “I get back to the set and nobody’s there.” he recalled in 2009, speaking to Vanity Fair’s Rebecca Keegan, reporting at the time for her book on Cameron, The Futurist. “I’m standing at the monitors, near the camera, and the room is empty. It was like the twilight zone.”

“Some people were laughing, some people were crying, some people were throwing up,” Paxton told Entertainment Weekly back in 1996. “One minute I felt O.K., the next minute I felt so goddamn anxious I wanted to breathe in a paper bag. Cameron was feeling the same way.”

Cameron remembers a Russian-Canadian P.A., who was working as a translator on set, summing it up succinctly: “I feel toxic and beside myself.”

The chaotic scene at the Dartmouth General Hospital makes for one of history’s best drug stories, even if the affected crew members didn’t know it at the time. “Eventually we all got put in these cubicles with the curtains around us, but no one wanted to stay in their cubicles,” set painter Marilyn McAvoy told Vice earlier this year. “Everyone was out in the aisles and jumping into other people’s cubicles. People had a lot of energy. Some were in wheelchairs, flying down the hallways. I mean, everyone was high!”

Cameron, who says he was stabbed in the face with a pen by a crew member (“I’m sitting there bleeding and laughing”), watched helplessly as his crew fell apart. “People are moaning and crying, wailing, collapsed on tables and gurneys. The D.P., Caleb Deschanel, is leading a number of crew down the hall in a highly vocal conga line. You can’t make this stuff up.” (Deschanel did not respond to a request for comment, but Paxton also described conga dancing—so someone must have been at the head of that conga line.)