I have been asked repeatedly to write River in the middle and while I wasn't originally planning a sequel for this, you win.
Several weeks passed since Jack had joined them on the TARDIS and while the Doctor had expressed interest in having a relationship with both of them in the beginning, he had avoided it. Jack and River agreed that that wasn't going to do. They flirted with him and tried to coax him out of his room as he hid from them. Finally desperate River decided another approach was necessary.
"Oh come on sweetie, I have always wanted to go to the man made caverns on Delta Six. They say the best time to dig there is in the year 7610." River begged him, just happening to "forget" it was the year after the great flooding that left most of the caverns a muddy mess. She pouted at him and he gave in. Everything was going fine until Jack slipped on a particularly slippery piece of ground and grabbed on to the Doctor for support. Surprised the two of them fell to the ground and Jack giggled as the Doctor looked up at him with mud covering his face. He pushed his hair back and his hair stayed as the mud held it in place.
"Sorry," Jack said as he got to his feet and then helped the Doctor up.
"It's all right, I suppose," The Doctor groaned. "We should head back to the TARDIS and get cleaned up."
"Oh now I won't get to dig for clues to the the civilization that lived her." River complained.
"I will take you to visit them," The Doctor huffed and started back towards the TARDIS. River winked at Jack and they followed him. Once aboard the TARDIS the Doctor disappeared quickly to his room and Jack headed to the shower as well. Sure that he had broken a record for the fastest he had ever showered he didn't bother to dress before he made his way to the Doctor's room and met River outside of it. River smiled at him and they made their way inside. The Doctor was still in the shower and singing to himself an opera song.
"Does he ever go quiet?" Jack asked and River shook her head. "Let's change that shall we." Jack kissed her softly on the lips and ran his hands down to help her remove her shirt. By the time the water was turned off they were both naked and River was kneeling in front of Jack. Jack groaned and ran his hands through her hair, guiding her speed.
"River," The Doctor exclaimed as he opened the bathroom door. "Jack." He held his clothes in front of his groin as his face turned bright red. River released Jack with a pop and then stood to look at the Doctor.
"Hello sweetie," she said as she got closer to him. His arms flailed and he dropped his clothes. He bent quickly to pick them up again and River grabbed them before he could. "You don't need these."
"River, I.." he stammered. Jack came up in front of them and turned the Doctor so his back was to the bed. Kissing him walked the Doctor over to the bed and then pushed him gently so the Doctor fell on it.
"That's one way to make him quiet." River smiled as she dropped to her knees. She took the Doctor this time into her mouth and groaned as Jack lined himself up behind her pushing in.
"River I have things I should be doing." The Doctor tried half-heartedly. Jack grabbed his hair pulling him up slightly so he could press their lips together once more as River moved between them.
"It can wait." Jack told him when they separated again and the Doctor nodded. He ran his hands down to River's breast and back up again as she moaned around him. The feeling of his hands and Jack moving inside her soon sent her over the edge and she screamed out her release. Jack followed soon after, spilling himself deep inside of her.
"Lay back further Doc," Jack told him as he pulled out of River. The Doctor was eager to comply at this point and moved to lay back on the bed. River straddled him and Jack moved behind her. He held River's arm's behind her back as the Doctor pushed himself inside of her this time. The Doctor was all ready close and his movements were short and rough. River screamed as she found a second release but the Doctor continued to move.
After the Doctor followed them over the edge, Jack released River's arms and she fell onto the Doctor's chest. Jack helped the Doctor to slip out of her before pushing himself back in. This time he took River slowly and gentle as she laid on the Doctor's chest. The Doctor ran his hands lovingly through her hair and kissed her gently. The flailing had stopped and the hyperactive Time Lord was quiet as he helped River reach her final orgasm of the night. Jack came once more inside her before collapsing onto the bed next to them.
"See what you have been missing sweetie." River mumbled as she kissed his neck.
"Yeah," The Doctor agreed his face relaxed and his half hooded in sleep.
"So when is it my turn?" Jack wondered with a smile.