Stiles and Isaac groaned at the same time, although Isaac's sounded far more shocked than Stiles'. He hadn't really given much thought to how the three of them would work, but he had never imagined that Stiles would fuck him. In a clear head, it would all make sense of course. Isaac had no interest at all in topping, actually hated the idea really. The idea of Derek fucking Stiles, while Stiles fucked him, however, made him harder than he could ever remember being. Isaac crooked his fingers, feeling the tension in Stiles' body give. He was tempted to stroke over the boy's prostate, but Stiles' hammering heart made him hold back. He didn't want this all ending too early.