⚠WARNING! SPOILER ALERT!⚠

I liked Girl, Missing and enjoyed Sister, Missing, but there's this thing that bothers me with Sophie Mckenzie's books. THEY'RE ALL THE SAME!!
The Medusa Project are my favourite and were the first books I read by Mckenzie, so afterwards when I read GM I couldn't help but feel disappointed that it was the same fast paced book with a main character who's too young to understand the consequences of their actions.
Then I went on to read Blood Ties and felt exactly the same. I read Blood Ransom and (shock horror) felt exactly the same. Nico (TMP) and Theo (BT/BR) felt like the same character to me and throughout BT/BR I constantly confused Theo with Nico. In Mckenzie's other trilogy, All About Eve, I even confused Luke with Nico! And Luke has blonde hair not brown!
Although there are those (minor) problems, I do love all Mckenzie's books and have read them all. I can relate to Lauren (the main character in GM and SM) and felt the loss at the end of SM when her biological sister Shelby died, despite her being horrible to Lauren, and I fell in love with Jam (James) who was Lauren's best friend until she realised they were more than that.
Overall, despite my problems, I loved Sister, Missing and think you should read it (granted you've read GM first otherwise it won't make sense!)

P.S Sorry if I've put you off!