The Worst Thing About Sister is a book by Jacqueline Wilson. It is about a young girl called Marty and her elder sister, Melissa. It is recommended for ages 9–11.
Martina "Marty" could not be more different from her sister. Marty is a tomboy who loves animals and drawing comics which feature a character she created, Mighty Mart. Her elder sister Melissa loves the colour pink, make-up and is very feminine. Their mum makes dresses and is a school secretary. Their dad is a travel agent who is losing most of his income because of the rise in online booking.
Marty is invited to Alisha's party just because her mum made a dress for Alisha. Her mother forces Marty to attend and makes a blue party dress. When she comes and picks her up she talks to the owner of the dancing school where the party was held. She announces that she wants her to make some costumes for the children and other parents want bridesmaids dresses. This means their mother has to expand - she needs an extra room to sew in so Marty and Melissa need to share a room. It gets decorated although most of it is chosen by Melissa because she's eldest. At school two mean girls called Ingrid and Katie call her Bluebottle because of the dress, so Marty sneaks in raw eggs and throws them resulting in some disastrous consequences. Marty invites her best friend Jaydene to look at her new room but acts like she prefers Melissa more than Marty, which annoys her. When Melissa shows her friends the room she is shocked to find Marty has trashed the room. Marty brings up some smoothies as an apology and is horrified to find out that Melissa is mocking her homemade animals. Marty embarrasses her by showing her friends Melissa's toy Baba and Melissa swears she will take revenge.
In the morning Marty can't find all her animals and the bin men had already been and presumes that Melissa has thrown them in the bin. Marty begins to pull off Baba's limbs but as a shocked Melissa climbs up the bunk bed ladder to get to Marty, the ladder breaks not fully on her but causes her to loose her grip and fall. Melissa gets taken to hospital where she is visited by Marty, who meets a young artist called Mattie. Marty and her dad return home and she finds her animals were under the bed all along. Marty sews together Baba and takes it to the hospital where Melissa is very thankful. The story ends with Marty saying how much she loves Melissa.
- Martina "Marty" Michaels - A young tomboyish girl who loves animals and drawing comics of Mighty Mart, a character that she created. Her mum always tells her off instead of Melissa.
- Melissa Michaels - Marty's elder sister who is very girlie, and likes the colour pink. She always fights with her little sister when they have to share a bedroom for the first time.
- Mum - Marty and Melissa's mum. She always gets cross with Marty for doing anything naughty, or for humiliating her sister.
- Dad - An estate agent who is Marty and Melissa's dad. He and Marty call each other Curlynob, because of their curly hairs.
- Alisha - A very fat girl who Mum forces Marty to attend her birthday party.
- Jaydene - Marty's best friend. Marty invites her to look at her room, but acts like she prefers Melissa more than her.
- Ingrid and Katie - Two mean girls who call Marty Bluebottle, because of her blue party dress.
- Mattie - A painter in the hospital who make friends with Marty.
- Wilma - A whale-shaped duvet cover that Marty bought at a school jumble sale.
- Jumper - A big black and white Dalmatian dog who is a very good guard dog for Marty's Marty Den.
- Basil - A boa constrictor made out of Mum's old tights and sewn a ferocious face at one end.
- Polly - A cardboard parrot who is brightly colored and fantastic at flying.
- Baba - A doll who belongs to Melissa. She can't go to sleep without her.