I never thought I’d end up here — naked, blindfolded, wrists bound above my head to a cold metal hook, my body trembling with equal parts fear and unbearable arousal.

My name is Sophie, and until two hours ago, I was the definition of vanilla. Twenty-six, quiet graphic designer from London, the kind of girl who blushed at the word “spank” and thought “kinky” meant keeping the lights on during sex. But after one too many lonely nights scrolling through forbidden subreddits, I finally did it. I booked a flight to Berlin, found the most exclusive underground club I could, and walked through the heavy black door wearing nothing but...