The religious siblings, bound by their faith and guilt, find themselves alone in the dimly lit closet. The younger brother's cock strains against his pants, visible to his older sister who can't help but stare. "We mustn't," she murmurs, yet her fingers trail down his chest, undoing his belt. He gasps as she frees his stiff cock, her hand wrapping around it. She strokes him, her thumb rubbing the pre-cum from his tip. He leans into her touch, his breathing growing ragged, as they both succumb to their forbidden desires.