Update: Wizards of the Coast gave more detail in a statement to Polygon that read, "As part of an investigation into the unauthorized distribution and disclosure of embargoed product, we repeatedly attempted to contact an individual who had received unreleased cards. After that outreach was unsuccessful, an investigator visited him and asked that he reach out to us as part of our investigation and return the embargoed product and packaging. He agreed to do both. The unreleased product will be replaced by us with the product he intended to purchase. We appreciate the individual's cooperation and the investigation is ongoing."
Original story: First reported by Polygon, a Magic: The Gathering fan and content creator with the handle oldschoolmtg had a rude awakening on April 23 when employees of the Pinkerton Detective Agency (yes, those Pinkertons), showed up at his front door to seize unreleased Magic: The Gathering products he'd happened upon in a recent haul.
Oldschoolmtg primarily does unboxing/overview videos for new Magic sets and limited edition products, and in a recent video (since taken down) sat down to cover some March of the Machine collectors' boxes he'd acquired. Included among the 22 boxes, however, was one set of March of the Machine: Aftermath booster packs, a follow-up to March of the Machine that doesn't release until May 12. Oldschoolmtg theorizes that the Aftermath set got mixed in at some point in distribution due to the similar-sounding names (I'm getting confused just writing this), while the contact he acquired the product from "is more of a Pokémon/Yu-Gi-Oh! guy" according to oldschoolmtg, and didn't realize what he'd stumbled on.
Oldschoolmtg showed off this effective early preview on his YouTube channel, which got picked up by other MTG content creators and eventually came to the attention of Wizards of the Coast. That's where the Pinkertons, contracted by Wizards, come in. The private detective agency is infamous in US history as a source of union infiltrators and violent strike breakers in the first great waves of labor unrest in the 19th century. Gamers may be familiar with them as Booker DeWitt's employer or perhaps the archnemeses of the Van Der Linde Gang (a portrayal the agency sued over, for the record). They declined in relevance as law enforcement practices evolved, but still exist today as a subsidiary of the Swedish firm Securitas AB.
Back to oldschoolmtg, the YouTuber surrendered the Aftermath set to the Pinkerton agents, who he describes as "big heavy hitter guys" who referred to the set as "stolen product" and warned him of potential arrest and legal action. Oldschoolmtg was put in contact with a Wizards of the Coast representative he characterizes as "nice and apologetic for making my wife cry first thing in the morning." Oldschoolmtg further explained that he will be at least partially compensated by Wizards of the Coast, and that the company wanted the product back primarily to help trace the leak in their own distribution.
Wizards probably could have just led with the polite contact and promise of compensation and saved the hard-hitting private dicks for if that didn't work. Regardless, oldschoolmtg and his family are fine, and if nothing else he's gotten some fresh attention for his YouTube channel to go with the conciliatory swag from Wizards of the Coast.