Here is a short story based on your prompt, written in English with an American setting, designed to be suspenseful with a strong twist.

The Hundred Dollar Betrayal

The notification lit up the dark living room like a lightning strike. My husband, Dave, was in the shower, and his phone sat innocently on the coffee table. I wasn’t the snooping type—usually. But the screen flashed a preview that made my blood run cold.

Sender: Unknown “Last night I spent $100 on you.”

The world tilted. My breath hitched in my throat. We had been struggling with finances for months, and here was my husband, apparently having $100 spent on him by some stranger? Or worse, had he paid for something illicit?

When Dave walked into the room, toweling off his hair, he found me standing over the phone, trembling.

“Sarah? What’s wrong?”

“Who is she?” I whispered, my voice shaking. “Who spent a hundred dollars on you last night?”

“What? I don’t know what you’re talk—”

I didn’t let him finish. Blinded by a cocktail of rage and heartbreak, I grabbed the phone and hurled it against the brick fireplace. The screen shattered into a spiderweb of glass; the device went dead.

“Sarah! Are you crazy?” Dave yelled, rushing to the broken pieces.

“Get out,” I hissed. “Sleep in the guest room. Don’t speak to me until you’re ready to tell the truth.”

For three days, the silence in our house was suffocating. Dave tried to explain, tried to say it was a wrong number or a mistake, but I wouldn’t listen. I was mourning a marriage I thought was perfect.

Then came the third morning.

I was drinking coffee, staring blankly at the rain, when the doorbell rang. By the time I opened it, the porch was empty—except for a woven basket.

Inside lay a sleeping newborn baby wrapped in a thick blue blanket. Tucked into the folds was a handwritten note. My hands shook as I picked it up.

“My son looks just like you. I can’t do this anymore.”

My stomach dropped. I dragged the basket inside, my heart hammering against my ribs. “Dave!” I screamed.

He came running from the kitchen. When he saw the baby, his face went ghostly pale.

“Is this it?” I cried, tears streaming down my face. “Is this the truth you were hiding? A child?”

“Sarah, I swear, I’ve never seen this baby before,” Dave stammered, backing away.

“Liar! The note says he looks just like you!”

I reached into the basket to check the baby, pulling back the blanket to see if he was hurt. That’s when I gasped.

On the baby’s lower back, just above the hip, was a birthmark. It was distinct, dark red, and curled perfectly into the shape of a snail.

I looked up at Dave, horror dawning on me. Dave had that exact same birthmark. Same shape. Same spot. It was a genetic quirk he’d always joked about.

“He has the snail, Dave,” I whispered, the fight leaving my body. “He has your mark. You can’t lie your way out of biology.”

Dave stepped forward, looking at the mark. He fell to his knees, but he didn’t look guilty. He looked… devastated.

“It’s not my son, Sarah,” he choked out.

“Stop lying! The text! The money! The mark!”

“The text…” Dave looked up, his eyes red. “Sarah, the text wasn’t from a woman I slept with. It was from Michael.”

I froze. “Michael? Your brother? You said he died five years ago.”

“He didn’t die,” Dave admitted, his voice breaking. “He’s in prison. Or he was. He got out last week. He’s an addict, Sarah. He texted me asking for help. That text—‘Last night I spent $100 on you’—he was rambling. He meant he spent his last hundred dollars buying a bus ticket to come to you… to us. He wanted to ask for money.”

“But the baby…” I pointed to the snail mark.

“Michael and I are identical twins, Sarah. We share the same DNA. We share the same birthmarks.” Dave gently touched the baby’s hand. “This isn’t my son from an affair. This is my nephew. Michael must have relapsed… he dumped the baby here because he knew I’d take care of him.”

I looked at the note again: “My son looks just like you.”

It wasn’t a taunt from a mistress. It was a plea from a desperate, broken brother who looked exactly like my husband.

I looked at the shattered remains of the phone on the mantle, then at Dave, who was now holding the crying infant close to his chest. The baby opened his eyes—they were the same hazel green as Dave’s.

“We have to find him,” Dave whispered, rocking the child.

I sank to the floor next to them, the anger replaced by a heavy, complex grief. I had smashed the phone, cutting off the only line of communication we had to the man who left this child.

“We will,” I said, placing a hand on the baby’s tiny back, right over the snail-shaped mark. “He’s family.”