I was 16 at the time and my step sister was a couple of months older than me. We'd known each other since we were about 3 and we were like real sisters as well as best friends. Anyway we were walking home from school and we both had to poo really badly but there was nowhere to go so we had to wait until we got home. I couldn't wait and I started pooing my knickers and I wet myself at the same time. I was so embarrassed but the relief was incredible. Lucy could tell I was embarrassed and she said she was too desperate to wait either and the next thing I knew she was pooing herself and a dribble of pee ran down her leg. I felt a lot better for that and as soon as we got home we ran the basement bathroom as it was more private than the upstairs one and we helped each other clean up. No one to this day knows what happened and it will always be that way.