With her mother in the back of the van

I am helping a friend of mine moving house during a hot summer day. She brought her mother and other friends to help her. As we packed everything into different cars, only a small place in the back of a van is left for my friends curvy beautiful mom an me. So she sits on my lap in the back of the car since it is just an hour overland ride. The others in the front can hardly see us because of all the cardboard boxes and furniture. I can feel her moms warm sweaty skin touching my legs as she is only wearing a thin slightly see-through summer dress. The smell of her hair drives me crazy. I am examining her skin, her strong thighs, her deep cleavage. I am totally sunk in my own fantasies. I am fighting that she won't notice. My pulse is rushing more and more. Suddenly she starts to gently stroke the inside of my leg...