Give Terri a better grip

Groaning as he felt the shocks of sexual pleasure shoot through his body. Instinctively, he moved his hand down and undid his fly. He wore nothing underneath, and so his cock sprang free. He closed his eyes, and all he could feel was Terri's hand slowly, and then quickly, and then slowly again, rubbing up and down his cock, up and down... he knew he couldn't take much more of this... and then he felt her let go. He opened his eyes, and saw Terri stepping back and Gayle walking forward. She sat down on his lap, nearly on his cock, face towards him, legs on either side of his. Her hand grasped his dick and he just about came in her hand there and then.
"If you want any more of this, John... you're going to have to do something for us." Gayle said, eliciting a giggle from Terri.
John couldn't believe this was happening. "What?" he asked.
The two girls looked at each other for a moment, and then Gayle looked back at John.