When Mel skips school to visit her mother's grave (she won't explain why at first) her teacher Mr Coleman decides it's time to pay a home a visit. Meanwhile, Brian has developed an allergy that causes him to sneeze and morph uncontrollably. Mel starts training Sophie to behave like a 'real' mother, while Lucy attempts to diagnose Brian's allergy. Unfortunately, during his visit Mr Coleman sees Brian sprout a new nose and ears, and resolves to return with their social worker. Josh is determined to hold a party to improve his social standing – could this somehow save the whole family from being taken back into care? Will the world find out Brian and Sophie are aliens?

Mel arrives home late and expects to be grounded by Brian and Sophie but isn't. She keeps trying to get into trouble until she comes home with a walkman she says she stole. Josh tries to get a date with Tanya Thomas (Zoe Thorne), so he enlists Brian's help. Brian morphs into Josh and asks out Tanya's friend, Denise, who fancies him. When the two girls meet each other on the day of the date, they both start hating Josh.

Lucy discovers she and her best friend are 'geeks' after they are the only two girls in the class not to be invited to a party. Mel gives Lucy a makeover, but this threatens to alienate her from Wendy, with whom she has been studying caterpillars. Sophie is struck down with a case of the flu, but enjoys her freedom from housework and responsibility and hides her recovery. Lucy decides friendship is more important than being 'cool', and she and Wendy discover that their caterpillars "were really butterflies all along."

Brian decides that he and everyone else should become a proper family so Brian enters a quiz night, however Lucy doesn't want to join so she goes to join Wendy's team and ends up playing against her family who will win and what will happen?

When Lucy calls Brian and Sophie "Mum and Dad", Mel gets angry and shows Lucy and Josh a box of things she kept to remind her of their real parents. However, a lipstick is missing from the box. Lucy realizes that it was she who had taken it and swapped it, so she must ask Josh for help. Meanwhile, after a string of Fs, Josh must resit his exams or be put back a year. To pay him back for helping with the lipstick, Lucy helps him revise, and discovers that he may be dyslexic.

Lucy finds an injured dog, which she names Dennis, and starts nursing it back to health. Mel disapproves, warning Brian that Lucy will be upset when it dies. Meanwhile, Josh spends the money he raised for a charity event on a football ticket, and starts to earn the money back by putting up 'dog found' posters for Mel. When Lucy finds out, she pays him even more to bring them all back again, by which time Mel has warmed to Dennis and agrees to keep him. However, Josh returns with a 'Have you seen Woolly?' poster and Lucy and Mel realize that Dennis, a.k.a. Woolly, needs to go home to the people who are missing him.