I started reading The 13th Sign thinking it is a young adult novel, however soon enough I found out it was a middle grade novel. I don't read much Middle Grade novels but I continued reading The 13th Sign because the synopsis sounding interesting, plus I am a sagittarius, just like the protagonist. Jalen somehow unlocks the 13th sign, Ophiuchus, and as a consequence, the personalities of everyone in the world shift depending on their new star sign. Logical, fair judges turn into emotional ones, diplomatic and rational presidents turn into hotheads and declare war; basically the whole world is crumbling and the only way it could be saved is if Jalen defeats all 12 signs and meets with Ophiuchus within 24 hours.
Thus, Jalen, along with her best friend and her best friend's brother, embark on this journey. The whole book passes by with Jalen fighting each zodiac and defeating him or her using her judgement of the star sign itself with the help of the Zodiac book she unlocked. In all honesty I found it a bit repetitive, different zodiac sign but same fight, and same result in the end, her winning. I know that is how it is supposed to go but I felt that is too simplistic, which is why I tend to not read Middle Grade books often. I didn't get much depth from the characters and I just hoped there was a bit more complexity in the end solution and some sort of shocking ending.
I do understand that this is a middle grade book and I would only recommend it to middle grade readers, because while I did enjoy this book, it isn't one I would recommend to strict YA readers. If Tubb ever writes a YA novel, I would definitely be interested in reading it because she is a great author.