As he stood with three friends and a few hundred strangers on an abandoned lot in Brewerytown Saturday, Michael Coad couldn’t help but wonder about the mystery person who brought them all there.

Was it a man or a woman who wrote the now viral letter prophesying that the only way to be saved was to become a “solid steel statue” or to “seal yourself in cement”?

Was it someone in the crowd who photocopied the missive and dropped it in Philadelphia mailboxes, asking the recipients to gather on that very lot on April 27 at noon?

“Was it Tin Foil Man?” Coad, 29, asked.

He nodded toward the person a few yards away, sitting on the grass and methodically wrapping himself in sheets of crinkled aluminum.

“Oh no, no,” Tin Foil Man, 22-year-old Andrew Jaffe, answered a few minutes later. “I’m just trying to find a way to procrastinate studying for finals. And $1.50 of aluminum foil, you know, it’s a way to spend a Saturday.”

Around him were others who heeded the nonsensical call: Come to the lot at 27th Street and Girard Avenue at noon April 27 to discuss “building a steel furnace” that would be used to mold people into solid statues. The writer – who titled his request “ABBA” – explained they were in danger because all the food they had eaten since first grade “is alive in your body.”

“Do attend,” the author, politely, closed.

Those who did attend packed backpacks and coolers of beer. One wore a yellow Hazmat suit and a gas mask, which he spoke through when a camera crew stopped him for an interview. A father and son from New Jersey prepared for the heat of the furnace with oven mitts on their hands. Flashes of silver were everywhere: a shimmering trench coat, hastily made aluminum hats, body glitter covering a man’s bare chest.

When ABBA’s “Dancing Queen” blared through the speakers, the crowd broke into song.

The letter had inspired countless internet memes, and Chris Barber on Saturday handed out copies of his own version: a 10-page essay exploring the letter’s meaning and message. Barber, a 30-year-old high school religion teacher, called it “a meme to the extreme.”

“If you really spend time with [the letter] you get a sense of an impending danger, a reason for that danger, what we need to do to get away from it,” he said. “It actually kind of holds together. And you have to fill in a lot of the blanks. But that’s kind of the fun of philosophy and religion in general.

“It’s worth reading,” he added, “even just for the fact that it brought together this community.”

Others in the crowd said the same, enjoying a reason to gather with people they might not have otherwise ever met. Still, some had mixed feelings, even a discomfort, worried that the writer of the letter might suffer from mental-health issues.

In anticipation of the party, nearly $2,000 was raised for charity through a GoFundMe campaign titled “Do Attend. Help a Friend.” A man in the crowd Saturday selling $20 T-shirts commemorating the day also planned to donate part of the proceeds to a group that works with those suffering from mental illness.

To the surprise of many, the man who wrote the letter did take part in the gathering. According to a reporter from PhillyVoice, who shared the exchange on Twitter, the writer, identified as Milton Jackson, arrived a few hours after the first attendees. In a wheelchair, he was accompanied by a friend from the neighborhood who said she had distributed the letter for him.

“We had no idea the letter was going to go viral,” she said, according to the video.

“It’s unbelievable," she added, looking out at the lot of people. "It’s beautiful, bringing people together.”