The girls left the mansion and went their separate ways...
Once home, Katie entered the shower and cleaned the muck and grime accumulated from the house from her body. She did notice that her breasts seemed tender and there was a noticeable irritation from her cleavage. Thinking nothing of it apart from an allergic reaction, she donned her nightie and went to bed.
It was 3:14am when she stirred. As she sat up in bed, something didn't feel right on her chest. She crept to the bathroom under the cover of dark, being careful so as not to wake her family. She relieved herself and approached the sink. Turning on the vanity light, she had to restrain herself from squealing as her eyes adjusted to the light.
She had not one, but two (minor) cleavages. Three breasts! The third one was a similar A-cup to her other two, but it was definitely present. Concentrating, she could feel a third nipple brushing against the fabric of her nightie. She pinched herself to check if she was dreaming... *ouch*... they were most definitely still there.
She removed the nightie and examined her... 'revised' chest. As she placed the nightie on the sink, she knocked over some of the items on the side.
"Katie, what's going on in there" asked her mum from her room. "Nothing mum, sorry..." replied Katie.