"I think you know what I would like to do"

I say, trying to sound as flirtatious as possible. Millie looks me in the eyes for a second or two, then pinches my arm and stands up, looking down at me saying:

"Well, I told my friend Rochelle that I would drop by her house today, so you could come with me if you want to?"

In my mind I'm thinking that a much better idea would be for Millie to let me play with her big tits instead, but out loud I say.

"Definitely, that'd be great."

"Great, let's go." Millie says and grabs my hand and leads me out the door to her car.

It takes us less than five minutes to arrive at Rochelle's house. It looks pretty similar to our cabin I think as we walk towards it. Millie knocks on the door, but there's no response, so after about a minute Millie knocks again, a bit louder this time, but still no response.

Millie thinks for a while, then says:

"Do you mind going to check if she's out in the back garden and can't hear us?"

"Sure." I reply, and walk around the side of the house and look around the corner. There, laying on a sun lounger, is a gorgeous brunette MILF with very big tits, and she is completely naked. I just stop in my tracks and stare at her for a while, then I see her hand moving on her pussy. She's masturbating!

I just stand there and stare at her. She has her eyes closed, and I am behind a bush so even if she opens her eyes she would not be able to see me.

About a minute passes, then I hear foot steps behind me, and Millie's voice asking:

"Is she there?"

"Shhh." I whisper to my step-mom and motion for her to come closer. Millie comes up next to me, and then sees that Rochelle is nude and masturbating a few yards away from us.

"Oh my god." Millie whispers in my ear, followed by:

"What should we do?"