I dressed in my borrowed (and kind of short) silk robe and walked straight back to the bathroom with the idea of filling the bath and having a soak prior to Sue's arrival. To my complete surprise when I entered the bathroom I found the bath already occupied by her naked little nineteen year old sister Traci smiling up at me from the far end of the tub.
The 'bath' was actually a hot-tub big enough for the whole family if they chose. The water was deep enough to lap Traci's neck as she sat on the tiled bottom. Looking down through the clear water I could see that like her elder sister this eager beauty who sat with her legs invitingly parted was also fully shaved.
"Hi, Mike," she purred, "I've been waiting for you." and she looked directly between my thighs where the sight of her was making me become fully aroused which was pushing my robe slightly out of shape.
Before I could make any comment on her being in the bath, Sue entered the bathroom dressed in a white bathrobe and looked straight at her sister sitting brazenly in the bath, and demanded, "What the hell do you think you're doing in there?"
"Waiting for Mikey," Traci answered sweetly.
"Oh no, you're not!" Sue growled, "I'm sharing this bath with him!"
"I was here first," her sister replied looking straight at me for support although for the moment I preferred to keep out of it.
"If you don't get out of that bath right now I'm going to hurt you!" Sue announced raising one fist.
Traci quickly got to her feet and also raised a fist as she faced her scowling sister and said, "If you hit me I'll hit you back, you bitch!"
"Why you little whore!" Sue snarled taking a step towards the bath. It was high time I got involved. I grabbed Sue by the arm to pull her back from the edge of the bath.
"Enough!" I said, "What the hell do you two think you're doing arguing over me like a couple of spoiled kids? Don't I have a say in this? You're sisters for gods' sake. If you both don't apologize right now I'm going to bed and you two can masturbate alone!"
Sue stared at me and then slowly turned to Traci and said quietly, "I'm sorry Traci."
"So I am I," Traci nodded, "I'll get out of here and let you have Mike's hard cock to yourself."
"There's no need," I grinned seeing the dejected look on her face, "Didn't your mother ever tell you to share your toys?"
There was a moment's silence as both girls looked at me and then at each other. Then huge grins of glee spread across their faces before Sue stripped out of her robe and stepped into the bath next to Traci.
She licked her lips with anticipation as she urged, "Well, come on, Mike, we're waiting!"
I slipped out of my bathrobe and joined the two naked girls in the water where we all knelt down close together with bodies rubbing erotically against each other. Two female hands reaching out to wrap round the shaft of my cock which brought it swiftly to full solid erection.
"Only one at a time?", Traci asked.
"No both together!" Sue answered eagerly.
"Take a big breath, Mike," she commanded, "It's underwater lovin' time!"
Since the day before when I had fucked Sue in the swimming pool, she just kept talking about underwater sex!
I gulped air and Sue pushed me backwards so that I slid beneath the surface of the water. She lifted my legs up and I sank all the way to the bottom of the deep tub. She promptly straddled my face to cover my mouth and nose with shaven pussy. I started to lick and lap at her hot little cavern before working directly on her clitoris - which was what I knew she wanted.
At the other end I felt Traci's submerged mouth close over my standing cock to take the head and half the shaft. She began sucking strongly for a few moments. The warmness of water sloshed against my shaft. She came up for air and without any hesitation straddled my hips and fully filled herself with my erect cock.