The Forgotten Wallet

“Sarah found an abandoned wallet on the subway. Inside, there were no cards, no cash—only a single note that read: ‘Don’t turn around.'”
She glanced over her shoulder instinctively, but saw nothing unusual. Curiosity got the best of her, and she took the wallet home. The next day, she noticed someone following her. Every time she looked, they were gone. As the paranoia grew, Sarah discovered another note inside the wallet that hadn’t been there before: ‘I warned you.’