When Mel skips school she won't tell anyone where she's been, which gets her in loads of trouble with her teacher Mr Coleman. She eventually admits that she was visiting her mother's grave, but by then it's too late - Mr Coleman has already decided to pay a visit to the house, and could easily find out that Brian and Sophie are aliens. This is made worse by the fact that Brian has developed an unexplained allergic reaction to something which makes him sneeze uncontrollably and morph odd body parts all over his face! While this is going on, all Josh is worried about is having a party at the house to impress the cool kids at school. But just when it looks like the party will have to be cancelled for sure, it becomes an unexpected way of saving Brian and Sophie from detection - with a little help from some fancy dress...