Riley turned around abruptly at the strange noise coming from the backseat. Since the car had bucket seats it was easy to see into the back, but it took her a few moments to understand what she was seeing. She was staring right at Bob's erection, hanging - that is, standing - right out of the top of his pants. Chrissie's hand was wrapped tightly around the shaft. After a few moments of staring at it she managed to raise her eyes up to look at their faces. Bob had his head laid back, eyes closed, trying not to make any more noises like the one he had just made. The pleasure he was feeling made that a difficult task. When she looked at Chrissie's eyes she was met with Chrissie looking right back at her, a mischievous grin on her face. She used her unoccupied hand to hold up a finger in front of her mouth, silently telling Riley to be quiet.
Riley looked quickly at Tony, who was busy driving the car. They had been singing along with music. He still was. He glanced over at Riley, who smiled back at him and pretended to start singing again. She hoped that he didn't notice her surprise or nervousness.
The four were good friends, and had been since high school. They hadn't been best friends, necessarily, but having graduated a couple years earlier, their friendship had lasted. Today they were coming back from a hike, driving down a back road towards home, when Riley had been surprised at the scene in the backseat.
Chrissie had been inspired by the normal sexual comments, the boner that had started forming in Bob's pants, and how easy it seemed to slip her hand under the elastic waistband of his sweats. She had slowly done just that, waiting for him to object, daring him to let her proceed. Bob didn't back down, but let her continue - much to Chrissie's surprise. She had just been teasing him, but when her hand touched his pubic hair, then the base of his penis, things got serious.